Buddhism

It's undeniable that within Buddhism, and Theravada Buddhism in particular, that monastic life is considered an aid to the path towards awakening, but it is false that Theravada teaches that nibbana can only be reached by monks, as Theravada scriptures mention several lay followers who were arahants.

some citations are provided here:

The Commentaries mention some lay followers who attained full enlightenment, including for example, Uggasena who was a lay man (an acrobat by trade) with the householder responsibilities with family and work as an acrobat in side shows. (DhA.iv.59‑65) The Commentaries also mention that Buddha's father Suddhodana died as a lay arahant. He became a Non-returner (anāgāmī) after hearing the Mahādhammapāla Jātaka (DhA.i.99; J.iv.55), and when he was about to die, the Buddha came from Vesāli to see him and teach him, and Suddhodana became an Arahant and died as a lay Arahant (ThigA.141).

https://www.dhammawiki.com/index.php/Lay_arahant

Again your mistake is to assume asceticism is necessary to realize nibbana, instead it is more that the monk's lives promote simple living in a way that is meant to help facilitate the path to realizing nibbana - but it is far from necessary, and it is not the asceticism itself that facilitates that - again, Buddhism famously rejects asceticism in favor of the Middle Path. I suggest you read more about Buddhism, maybe try What the Buddha Taught by Walpola Rahula.

The practices the bhikkhu follow are meant to increase the odds of realizing nibbana happening, but according to Buddhist scripture, nibbana was also realized by lay followers who were not monks and who did not live ascetic lives.