Honestly, I had never thought about this before, or at least I don't remember thinking about it.
Say that Foundry USA, AntPool and F2Pool (which in total hold about 69% of the hash rate according to
btc.com) cooperated to pretend there's network congestion, when there isn't. For example, say the median fee is 1 sat/vb. But, they don't like that, so they broadcast a thousand transactions paying 5-10 sat/vb, to encourage some of the users with 1 sat/vb to raise their fee rate. Pools' transactions don't cost them anything, because they don't include them into their candidate blocks. They just take advantage of the wallet software there exists which tells the user to pay more to have priority.
This isn't limited to when there isn't congestion. Pools could do this right now with Ordinals, and broadcast transactions with 100 sat/vb; that would encourage those paying 50 sat/vb to raise fees. To avoid other pools from including their transactions (and pay 100 sat/vb which is pretty high), they could sometime include a transaction that invalidates their attractive transactions (e.g., spends an UTXO from those).
A problem, from the pool owners' side, is that they can get caught easily for doing it. Every person running a full node will notice unreasonable activity (the miner not including tx that pay much), and blocks mined by pools are known.
firstly..
pools dont need to broadcast unconfirmed tx to a network but then not include them in their own block template.. you have it the wrong way around
a productive method of fee mania is the opposite.. its to not broadcast unconfirmed transactions to the network. so that other pools dont add an attacker pools tx to their block.. but only include high fee tx in their own blocktemplate.. that way the transactions dont end up in a competitors block and only be in the creators block thus whatever fee the pool puts into its own transaction it gets back . thus no loss no cost.
if you did do things your way to broadcast unconfirmed to network but refuse to put your own transactions into your own block template.. then you wont get your fees back and you instead would pay some other pool when they include your transactions in their block. thus cost you alot to do it for "thousands of transactions"
secondly pools dont need to use ordinals to set high fee rates. pools can just put their own transactions into their own blocks (not relayed before block solve.
there is no need for ordinals at all to be used for fee mania..
the only purpose of ordinals is data bloat by putting in stupid 3.96mb meme images to stop normal users transactions from fitting into blockspace because its used up
lastly.. many fee estimators base it on a recent set of confirmed blocks fee amounts. so its more about the fee of the last few blocks. rather than whatever transactions are being relayed around which you hope will never get into a block.
so again if you want to cause a fee mania you have to put transactions with high fees into a block