In Jainism this mainly depends on sect (Digambar / Shwetambar) and on Jain rules about women’s ascetic life, not on “less spirituality” of nuns.

1. Shwetambar tradition

• Name itself means “white‑clad”.
• All renunciants – monks and nuns – wear simple white clothes.
• So here the question “why don’t nuns go sky‑clad?” does not arise, because even monks are not sky‑clad; their ideal of renunciation allows basic clothing.

You can read a simple comparison here

2. Digambar tradition

• “Digambar” means “sky‑clad” – the ideal for male munis is complete renunciation, including giving up clothes.
• For women, Digambar tradition has a different monastic path:

- Women take Āryikā / sādhuvī dīkshā (nuns). - They wear very simple white clothing.

• Reasons in traditional Digambar view:

1. Practical & social protection – a woman’s nakedness would create strong disturbance in society; this would obstruct the calm, non‑disturbing life required for a Jain ascetic. 2. Doctrinal position – Digambar ācāryas say that the specific sky‑clad muni‑dharma (including total nudity) is prescribed only for men; women can follow very high vows as āryikās but are not given that exact form of muni‑dīkshā. 3. View on moksha – classical Digambar doctrine says a woman must take birth as a man before final liberation; therefore, the last birth’s muni‑state is described as male and sky‑clad.

A short explanation of this difference is here

3. Essence in both sects

• In both Digambar and Shwetambar, the main point is:

- Non‑violence (ahiṃsā) - Non‑attachment (aparigraha) - Control of mind, speech, body

• Whether clothed or unclothed, a nun practices:

- Mahāvrat (great vows), - Hard discipline, - Study, meditation, and tapa (austerity).

So nuns do not follow sky‑clad practice because their traditional Jain monastic rules are different, especially in the Digambar line, while their inner goal and vows remain the same path towards moksha.