However, this fee is levied on all member banks of FDIC, which is basically every bank. Thus, it creates the most natural ground for collusion, i.e. everyone implicitly agrees to pass on the fees to the customers.
More than that, a bank account is probably one of the stickiest "purchases" an average individual makes in their lives, unlike a single-use water bottle. How many people do you think has the time and energy to switch to a new bank every time there is a fee increase? Is it the individual's fault for not doing so?
Would you notice a 5 basis point change in your savings account?
How many grains of sand do you need to stack before it becomes a pile?
As you say, the what really matters is (perceived) elasticity. If a company thought they could increase profit by increasing prices then they'd just do it. Conversely if they get fined or regulated or whatever but, as expected, it doesn't affect their elasticity curve then they'll leave prices where they are. If they were acting rationally it was already at the ideal point.
To me it felt like the market collectively decided "this is a good time to squeeze our costumer and have them blame somebody else"
That assumes banks balance this liability by reducing payments to customers rather than reducing profits. That's a common and completely misleading claim by businesses - if they are taxed or fined, they pass it on to their customers (obviously, it's an attempt to create political support for the business).
The reality is that the ability to raise prices (or lower interest rates on deposits) depends on the elasticity. If you raise prices on your bottle of water at the supermarket, then people will just buy the bottle next to it - the water-maker will be paying and fee or tax increases out of their profits. If you have the only bottle of water in the desert, you can charge whatever you want. I would think that regular savings deposits, at least, are easily moved to another bank.
Another consideration is that if they could squeeze more out of customers, they'd probably already be doing it. By that theory, at least, they've already optimized or that and can't charge more.