If Buddhas don't feel bliss, what is the purpose of attaining nirvana?

In the context of this question, eg there are differing types of concepts described by the same English words, many of the exact concepts nothaving exact English equivalents. Nonattached kindliness & nonattached compassion, & lovingkindness are sometimes utilised more at more existential concepts and existential nuances.

Many books talk about the subject of this question, and many words written about it, however, sometimes the concept seems oversimplified because of the words. Readers often infer, and very reasonably so, the fairly standard definitions for the words, when in fact there may be specialised meanings intended to be implied.

Some 'concepts', eg some existential concepts arent'very easily described using fairly standard English words. Yet many contributions to understanding of the concepts may be assisted by descriptions of features of the concepts for which there are more well known English word equivalents, and an example of that might include the subject of the question:

One aspect of Enlightenment is that there's lack of illusion, & there 'is' Reality, & there isn't confusion or illusion or cloudiness or dukkha. There isn't illusion or cloudiness. Things are 'seen' correctly & as they really 'are', & Kindliness & compassion & niceness are without attachment! And kindliness & compassion & niceness are for benefit to other beings rather than for personal, or to go to a heaven, etc

Why ask why?

Just be compassionate and understand that people have created their own worlds, from past lives, and that they are born with mental projections as part of the karma they need to work through. Try not to get pulled into bullshit when other people are chasing their own tails around, in a ball of confusion. In other words, if people refuse to listen to your calm purity, don't chase them down and try to force wisdom down their throats. They'll spit it out.

Love all sentient beings, but also your self. Be kind to others, but also to your self.

But I realize I have not answered your specific question. The purpose of attaining nirvana--Is this a serious question? All people must achieve it. It is the purpose of living. No one is excluded from this goal of self-purification.

I'm pretty sure I know the answer to this: no-one knows.

You can only read the metaphors about extinguished lamps etc. to get it.

See Collins' Nirvana: it is an excellent piece of scholarship -- from a Theravadin perspective.

Being enlightened as ''having love and compassion'' is from the people who cling to the dichotomy hate-love. They heard that Being enlightened means having no hate, so they think that Being enlightened means being full of love.

More generally this stems from their lack of understanding that four Brahma Vihara or four sublime states [ metta (loving kindness), karuna (compassion), mudita (sympathetic joy), and upekkha (equanimity) ] is not being enlightened.

It is the jains and hindus who keep saying that having compassion means '' consider their suffering as your own is general-compassion.'' https://www.wisdomlib.org/definition/anukampa

So the buddha has anukampa, ie compassion, and he says he teaches out of anukampa. The buddha did not get enlightened because he wanted to be full of love and be compassionate. THe buddha wanted to end dukkha and the result is the ending of dukkha and he teaches out of anukampa. Even Ananda says he answers the nuns out of anukampa. The usual paragraph with anukampa is like this https://www.accesstoinsight.org/tipitaka/mn/mn.152.than.html

"So, Ananda, I have taught you the unexcelled development of the faculties in the discipline of a noble one; I have taught you how one is a person in training, someone following the way; I have taught you how one is a noble one with developed faculties. Whatever a teacher should do — seeking the welfare of his disciples, out of sympathy for them — that have I done for you. Over there are the roots of trees; over there, empty dwellings. Practice jhana, Ananda. Don't be heedless. Don't later fall into regret. This is our message to you all."

Mn152 also explains how enlightened people view feelings, tactile sensations and so on.

Nibanna is bliss, but not bliss with the senses, not even the bliss from the jhana. It is the other kind of bliss and you can't know it before being enlightened.

From AN 9.34:

Ven: Sariputta: “Reverends, extinguishment (Nibbana) is bliss!

Ven. Udayi: “But Reverend Sāriputta, what’s blissful about it, since nothing is felt?”

Ven. Sariputta: “The fact that nothing is felt is precisely what’s blissful about it.

Sukha or happiness for an unenlightened person is experienced when encountering pleasant feelings (from the six senses, including thoughts and the intellect) or when encountering the cessation of painful feelings (from the six senses).

But for a Buddha or arahat, sukha or bliss (in this context) is experienced when encountering neutral feelings, no feelings and Nibbana.

Please see this answer for commentaries by Nyanaponika Thera. The supporting suttas are MN 44, SN 36.5 and AN 9.34.

In addition, the Buddha and arahats can experience emotions or states of mind which are not tainted with the three poisons of greed (lobha), aversion (dosa) and delusion (moha). This includes the four brahmaviharas of loving kindness (metta), compassion (karuna), empathetic joy (mudita) and equanimity (upekkha).

The brahmaviharas are considered skillful states of mind.

An enlightened person is not an emotionless person. It's simply a person who does not have cravings, does not have plans to fulfill sensual cravings, does not have plans to become something and does not become afflicted with negative states of mind that arise as a side effect of having craving. Also please see this question.

The purpose of Nirvana is permanently ending suffering - it's not about experiencing bliss.

Adding on based on a comment by Ruslan, the Buddha did have his five aggregates (form, feeling, perception, mental formations and consciousness) intact and functioning without being tainted by the three poisons, after attaining Nibbana, and could still experience pain and pleasure, but did not suffer from it. Please see this answer for details.