pools cant change bitcoin rules. only devs can when devs make node upgrade options. so it was the devs that removed the fee formulae
You're confused about what "Bitcoin rules" are. Transaction priority was never a consensus rule. It was a client side rule. Not required by the protocol. That's why there was no fork when miners (and later Core) removed it from their clients.
1. pools cant change the rules.(separate debate)
2. pools can IGNORE features that are not ruled(separate debate)
3. but ultimately it was the core devs that REMOVE or add code
EG pools still ran CODE that included the fee priority. they just ignored it. they didnt release a node to the public that didnt include the fee priority.
pools did not release a node to the public.
it was the core devs that did.
so while pools were ignoring the fee priority, users were still getting messages about fee priority issues. until CORE removed it
ultimately though a new better fee mechanism can solve the issues you have of:
thinking blocks need to be stifled just to get people to pay
thinking pools wont get paid if blocks were large and demand was low
knowing the math that 1mb baseblock 2mb baseblock 4mb baseblock is not a harm to decentralisation..
knowing the math that 1mb, 2mb,4mb base block is no harm to miners
knowing the math that fee's are not essential for years/decades
knowing a fee priority formulae can be implemented to solve the previous 2 things when pools need fee's.
there is no reason to keep blocksizes low under the ruse of "helping pools"