Legality of Bank Inactivity Fees

I hadn’t been paying attention to my checking account (in which I kept a minimum balance
of $1500 just to avoid a monthly "maintenance fee") for about a year. But, yesterday I
logged in and found that it had incurred a $5 "dormant fee" in each of the last 4 months.
I newly learned that a checking account becomes "dormant" after 11 months without activity.
This bank is in Washington state in USA.

I could have avoided the fees simply by moving $5 from my checking account into my savings
account.

It frustrates me that they never even sent an email to me (before or after any of the fees).

Is this really legal in USA?

In court, I would argue that the bank actually benefits from my inactivity.
Accounting is easier and, for a given total balance, they would actually prefer
to have inactive customers for more stable loaning. They simply did not provide
anything, or incur any extra difficulty, to justify a fee.

It is clear that they are taking advantage of fine print that no one ever reads,
about a fee that the customer does not naturally expect. I consider this to be
morally wrong, but wondering here if a class action lawsuit is likely to win or lose.