In Jain tradition, Jambuswami was the last kevalī of this avasarpiṇī era. After him, no one attained kevalgyan because the conditions in the world became less and less favorable for such supreme spiritual realization.

Main reasons are:

1. Kāl-chakrānuṣār decline

In avasarpiṇī, dharma, strength, lifespan, body, memory, and spiritual capacity gradually decline.

1. Very rare causes for kevalgyan

Kevalgyan comes only when all ghāti karmas are completely destroyed through perfect: - samyagdarshan - samyagjñān - samyakcharitra - intense tapa and purity

1. No suitable spiritual era now

After Jambuswami, the world no longer had the same purity, discipline, and inner power needed for that highest state.

So, in short: not because kevalgyan became impossible in principle, but because the time-cycle and conditions after Jambuswami were no longer favorable for it.

If you want, I can also explain this in simple Gujarati or Hindi.