- High bandwidth usage

- Relay operators need to get paid, and the typical user currently pays for centralized services by sharing their data. Paying for multiple relays will not be accepted by these folks.

- Instead of one evil corporation having your data, everyone has access to your notes, etc.

- Privacy was never a consideration in the protocol design

- NIPs are a moving target. People have been attempting to implement private (secure) chats and marketplaces, but have to keep rewriting and redesigning what they just released.

I'm sure if you spend a few minutes, you can think of other issues, unless you're a new user.