Why do banks give checking account promotions?

Hello. I would like to know why a bank would consider it worthwhile to give me $300 for free when I open a checking account and do a few direct deposits from my workplace there.

I have done this with several banks, repeatedly over many years.

When I ask this question to the banker, they tell me one of the following ideas which do not seem worth the $300 investment that a bank would make in me.

The first idea is that the bank wants me to form my relationship with them so that I will do my home mortgage loan with them later and then they can make money from the loan fees etc.

The second idea is that the bank wants to catch fees from me in the form of cashiers check fees or wiring money fees or brokerage fees or overdraft fees.

The third idea is that the bank wants to rapidly increase the number of customers it has in order to look good in some kind of bank rating system, in order to attract investors or something like that.

What do you think: do any of these ideas seem like it would make it worthwhile for the bank to give me $300?

Often I pursue the bonus blatantly, politely telling that banker that I am here because I want the bonus. And then when I close the account I tell the banker that I just wanted the bonus. The bank has to know that a punk like me with my history is not going to make them any money with fees or loan business.

And yet I get a flyer in the mail every few years encouraging me to open a new checking account to get a $300 bonus. At the same bank where I just closed my checking account two years ago.