Okay... I don't know what exactly your problem is, but actually I don't really care. Just because you (allegedely) never had any problem with the Immigration about this, that doesn't mean that's the standard for everyone. You were supposedly always lucky, others had to pay... end of the story. Have a good day...
As I said... it "might" happen... some people got fined, most not. It depends, as usual, on your local Immigration office and/or the mood of the officer that day...
As Andy said... they don't care at the border (in/out), but... if you ever go back to the Immigration Office for "whatever" (Certificate of Residence, Extension of stay, changing Address, or, or, or...) they might see in the system that you failed to report... so it might happen that they make you pay... or you may be lucky... it depends... 😁
Not, if you ask the banks now... it's "just" a visa for 90 days. What they want to see is the one year extension to open an account... bad thing is, that you need the bank account first to get the extension... catch 22... welcome to Thailand... 😁