Why are Buddhist monks not as extreme as Jain monks when it comes to non-violence?

Good householder. There are "many" monks who would abstain to sweep the soil, fearing to 'dig' into it or useless harm and kill. There are also those using a broom. However, hypocritical moral has no place within the training, yet it's for sure not easy to know ones mind, especially if not Noble yet.

But wouldn't it make sense for the Buddhist monks to be as extreme as Jain monks as they also try to avoid harming any living thing?

Buddhism is famously a "Middle Way" (Wikipedia), which is said to mean, "avoiding the two extremes".

That Wikipedia article mentions that there are suttas which criticise the Jains for some of their relatively extreme practices.

That said there are rules for Buddhist monks to avoid harming living things -- for example they are not to dig earth (unless it's clean gravel or sand or something). And I think there is sweeping in some places, to keep the paths clean, but I suppose it's situational, and is not a ritual to be practiced always (in fact, "rites and rituals" in general is considered one of the "fetters").

Mahavira aka Nigantha Nataputta, the founder of Jainism, taught that physical karma is more blameworthy than mental karma.

The Buddha however, taught that all karma begins from the mind, thus it is mental karma that is most blameworthy.

“Nigaṇṭha Nātaputta describes the physical rod as being the most blameworthy for performing bad deeds, not so much the verbal rod or the mental rod.” .....

“I describe mental deeds as being the most blameworthy for performing bad deeds, not so much physical deeds or verbal deeds.”
MN 56

This can be found in the verse from the Dhammapada:

All mental phenomena have mind as their forerunner; they have mind as their chief; they are mind-made. If one speaks or acts with an evil mind, 'dukkha' (suffering) follows him just as the wheel follows the hoofprint of the ox that draws the cart.
Dhammapada 1

The commentary to Dhammapada 1 tells the story of Ven. Cakkhupala, a blind elder arahat monk who accidentally and unintentionally killed some small insects by stepping on them.

The Buddha said that Cakkhupala did not have the (mental) intention to kill the insects, hence he was not guilty of it.

However, based on Jainism, mentally intending to kill insects without actually performing the act is not as bad as accidentally killing the insects without mentally intending to. Or at least this is the case, according to MN 56 (quoted above).

In MN 101, the Buddha debunked the following teachings of the Jains:

• All the happens to a person is due to past karma
• Elimination of past karma is possible by penance
• Elimination of karma is possible by not accumulating new karma
• With emptying of all past bad and good karma, suffering would end

In other words, the Jain way is emptying the karma account in order to end the cycle of rebirth, which is suffering.

The Buddha's path is that of the purification of the mind to end suffering, and not emptying of the karma account.

The Jain idea is that suffering is sustained by karmic balance. The Buddhist teaching is that suffering is sustained by craving and ignorance.

“Mendicants, there are some ascetics and brahmins who have this doctrine and view: ‘Everything this individual experiences—pleasurable, painful, or neutral—is because of past deeds. So, due to eliminating past deeds by mortification, and not doing any new deeds, there’s nothing to come up in the future. With nothing to come up in the future, deeds end. With the ending of deeds, suffering ends. With the ending of suffering, feeling ends. And with the ending of feeling, all suffering will have been worn away.’ Such is the doctrine of the Jain ascetics.

I’ve gone up to the Jain ascetics who say this and said, ‘Is it really true that this is the venerables’ view?’ They admitted that it is. ...

But since you don’t know any of these things, it’s not appropriate for the Jain venerables to declare this.’ ...

Such is the doctrine of the Jain ascetics. Saying this, the Jain ascetics deserve rebuke and criticism on ten legitimate grounds.
MN 101

Buddhist monks aren't practicing properly if they willfully commit bad karma to save time. Whatever practice is done in that saved time would be done on top of bad karma. The more bad karma a practice has behind it the more likely it leads the practitioner towards suffering and away from wisdom.

In the Buddha's teaching, any action that involves karma comes with volition (cetana). Action without volition is neither bad nor good. For example, the blind monk, Cakkhupala, killed some insects while doing walking meditation. He did not have the volition(cetana) to kill any insect so no bad or good karma would have arisen. Even though Cakkhupala stepped on them, no bad intentions arised. In this way Cakkupala did nothing wrong.