Savings accounts that have a signup bonus but offer close to 0% interest rate. Are they hoping you will just put the money in and forget about it? Is that how they make money on it?

Curious- small banks. They offer a little bonus to join (maybe like 200 USD for 15 debit card transactions) and eat a little loss up front. Do they make money just based on their location/being very convenient for locals to use?

What's stopping someone from just switching to a bigger bank (for the convenience nationwide, more ATMs and support, etc)