No logic or reason behind it, and no attempt to be better at any particular thing, just a mindless protest at centralized platforms.
A bit dismissive... :) The nostr first presentation explains quite well what, why and how.
Did you know that every DM you send is making your key weaker too? Most clients are still using NIP04 and now those keys are compromised if users sent a lot of DMs.
You are right kind:4 messages suffer a crypto problem, this sucks, but to be precise and fair, this impacts "only" the DMs itself, not the full key; the theoretical risk is to leak the previous conversations. When the new protocol (NIP-44) is in place, clients will adopt it, and users will have a new robust private channel with the same key.
Note: I am not an expert in cryptography by any means, I am just following the discussion.