Two traditions within Jainism explain this differently:

• Digambara (the sky-clad monks): The Teerthankaras are depicted and understood as sky-clad (nude) when they are complete renunciants. The nudity symbolizes complete detachment from all worldly possessions.

• Śvetāmbara (the white-clad monks): The Teerthankaras are depicted wearing white garments. They renounce possessions, but they may wear simple white clothes as part of their renunciation and daily practice.

So, the difference is regional/sectarian: nude in Digambara, clothed in Śvetāmbara. Both view the Teerthankaras as perfected beings who have conquered all attachments.