Why activity makes me material & full of desires?

I have never read anywhere in the Pali scriptures where the Buddha threatened lay people with continuous cycles of rebirth or urged lay people to end rebirths. In the Pali scriptures, I have only read the Buddha teaching the path to 'heaven' for laypeople.

The Buddha taught lay people to work with initiative & energy; to make enough money to support themselves, their family & others.

In this current globalized & dynamic world, you must be efficient. Discipline & non-attachment can help.

"So how can I be active & aspirant to dissolve Dukkha/future births simultaneously?"

You cannot do it simultaneously.

If you're active, you must think. With thinking, there is no meditation. Thus, no dissolving of Dukkha/future births.

If you're not active, you can stop thinking. Without thinking, there is meditation. Thus, yes dissolving of Dukkha/future births.

Ask yourself what is more important to you? Then do just this one thing and let the other not be a priority.

Whatever you choose, either being active or not being active, you will come to not being active.

Why is this so?

By choosing being active, sooner or later you will get all your desires satisfied.

If not in this life, it will be in the next. Or the next. Or the 100th.

In this satisfaction, no happiness will be found. In satisfying your desires, you will find only happiness that leads to suffering. Constantly circling and going from suffering to happiness and vice versa. This is what satisfying desires leads to. This is the result. This is the truth of satisfying desires.

Once you realise the above truth, you'll let go of desires. Thus, you'll let go of materialism.

Then, you'll live your life modestly, without aquiring to much nor to little and do what is left to do: become not active.

Meditation will happen. Whatever you choose.

It appears you may not be meditating while you are active, therefore not actually seeing the material desire as it arises in the moment, only knowing about it retrospect, which produces regret, guilt and suffering. If you can see how your mind constructs these material desires in the moment, you will be better equipped to let them go over and over every time they arise. Stop thinking about meditation as an adjunct to life. It is life. Develop mindfulness at all times.

Meditation involves withdrawing from sense desires. Being active and being mindful is possible, if you develop sufficient base level of mindfulness and equanimity by practicing it ardently so that you are not taken over by your desires when interacting with the world.

But your question is not that, is it? It seems to me that while you in principle accept that meditation is the way forward, you cannot bring yourself around to give up the worldly pleasures. So your question in essence is "Do I do the boring meditation or get excited about the world and the riches it offers? One way there is an end, but the path appears to be boring while the other is exciting but without any end in sight"

Its not easy to give up on pleasures, or the process of becoming, identification. What you can do is develop insight into this, and see for yourself what these drives are made of. When you feel the excitement, ask yourself what is it made of? Is it permanent or transient? Will it bring me the promised pleasure or will it leave me high and dry, in want of more like an addict needing another fix? Will attending to these desires bring any satisfaction, release or will I be perpetually a slave to it?

See for yourself that these drives are transient, unsatisfactory and without any essence. That in essence is mindfulness. And that leads to unbinding from the samsara and dukkha.

Because you have not dissolved the Hindrances, Afflictions, and not attained Awakening. These fires are active in all people.

Instead of taking the restrictive and simpler path: the Theravadin path of becoming a monastic.... most of us have to choose to take the Mahayana path--the path of attaining Awakening within the world of Samsara which has become more complex in nature. This is the path of Bodhisattva and produces a superior class of Enlightened beings as compared to the Theravadin path whereby such people cannot keep their peace within the world. But unfortunately, in some ways this path is harder than ever (more desires).... In other ways this path is easier now than ever (technology, facilities, conveniences, GTD).

Keep practicing and learn to not add attention/energy to fires.

What really matters for a lay person as per Buddhist teaching is whether you are at least a Sotapanna which assures you the enlightenment withing seven births. As far as you have the right livelyhood you do not have to worry being materialistic and being rich.

Sometimes during meditation, a noisy drill or something will start up from outside. Those times are great because you really get to see whether you are able to meditate or you just like the pleasure of tranquil sitting (I am not lazing! I am meditating!).

As long as the job itself conforms to right livelihood (samyag-ājīva / sammā-ājīva), it does not in of itself contradict the dharma.

It is not a problem to want to earn a lot of money. It takes a lot of smarts to be able to do so and you can do a lot of good for a lot of people with a lot of money. The answer lies in your motivation, what you want the money for. Engineers like to solve problems and make things work. Sales people genuinely like interacting with other people. You will have your own vocation.

Let a man, after he has discerned his own duty, be always attentive to his duty.
Dhammapada XII.166

To study, to work, to make a difference, to "light up a corner of the world", these are all admirable things. To please yourself with temporal goodies of all kinds maybe not so much, although:

He who, though dressed in fine apparel, exercises tranquility, is quiet, subdued, restrained, chaste, and has ceased to find fault with all other beings, he indeed is a Brahmana, an ascetic (sramana), a friar (bhikshu).
Dhammapada X.142