Spam protection with blobs

Something I've been wondering about…
So currently blobs are priced cheap, but rollup users are willing to pay more (because they did pre 4844). So block proposers who want to swap up max fee can simply spam useless data. This way they can make the fee go up. Sure it will cost them a bit but as long as they offer a price that is just below what the market is willing to pay they should still profit…

Am I missing something?