Everywhere I read tells me it is not a good idea to leave BTC long term at an exchange wallet. However, the same people who say that recommend crypto interest earning accounts such as BlockFi or Celsious. Doesn't make sense to me. So I should not trust Coinbase or Gemini yet I can trust BlockFi or Celsius to keep my crypto safe? What?
Yes you have learnt well; it is not advisable to store your bitcoin or any other crypto currency assets on your exchange account because it is centralized and not your own wallet; the best way to store your assets is on your paper wallet or your cold storage and also ensure not to share your keys or phrases loosely.