Short answer in simple words:

1. Not all Jain munis are without clothes

- Digambar munis (sky‑clad) – do not wear clothes. - Shwetambar munis – wear simple white clothes.

So “muni don’t wear clothes” is true only for Digambar male monks.

1. Main reason – complete renunciation (Aparigraha)

Digambar acharyas say: a true muni should not possess anything – no money, no utensils, not even clothes. - Clothes are also a possession. - Where there is possession, there can be attachment and fear (losing it, keeping it clean, good looking, etc.). - By giving up even clothes, the muni shows: “I have nothing, I want nothing from this world.”

1. Symbol of total detachment (Vairagya)

- The body, heat–cold, respect–insult, praise–criticism – nothing should disturb a true sadhu. - Living without clothes is a constant tapas (austerity) and reminder to stay detached from comfort and shame/ego about the body.

1. Following the example of Tirthankars (as per Digambar view)

Digambar tradition believes that Bhagwan Mahavir and other Tirthankars finally lived without clothes after full renunciation. So Digambar munis try to follow that same ideal of sky‑clad life.

1. What about Shwetambar tradition?

- Shwetambar munis and sadhvis wear simple white clothes. - They say: clothes can also be used without attachment, just as a basic cover, while still practicing full vows and inner detachment. - So goal is same (moksha, non‑attachment), expression is different.

In short:

• Digambar muni: no clothes = sign of absolute non‑possession and detachment.
• Shwetambar muni: simple white clothes = minimum possession, but focus on inner non‑attachment.

You can read more in very simple language here: “Why does jain muni not wear any cloth”