Short answer: Digambar murtis are shown nude because in Digambar Jainism the Tirthankaras are viewed as having renounced all possessions, including clothing, when they attained kevala jnana. This is why their iconography is sky-clad (nirgrantha) and their idols are depicted as unclothed. In contrast, the Śvetāmbara tradition tends to depict Tirthankaras clothed (aṅgī) as a symbolic representation and for reasons tied to their own interpretive tradition.

Key points:

• Digambar view: Tirthankaras practiced extreme renunciation and remained nude; the naked form symbolizes non-attachment and spiritual purity.
• Śvetāmbara view: Tirthankaras are often shown clothed, reflecting a different symbolic emphasis and tradition.
• Historical context: The two sects developed different interpretations and iconographic conventions over time, and both honor the same Tirthankaras, just represented with different garb.

If you’d like, I can look up a specific Jain Knowledge page that explains the nude (nirgrantha) iconography of Digambar murtis and the clothing of Śvetāmbara murtis.