In my humble opinion, this mempool attacks are done by miners, this happened also during the China Mining Shutdown (first half of 2021) or by people who want high fees and impede mass adoption.

Supose 1 block = 1Mb data @ 1 sat/byte = 10 485 76 sat = 0,01 BTC (tx fee) / block

With sufficient spam blocks (50K) the average price/sat is then increase 10x (in fact much higher), for each block you mined, you get back the cost of 10 blocks spammed.

In case the attack is against the network itself the cost to have 50Mb mempool = 50 blocks is 50 x 0,01 = 0.5 BTC = 12500 USD

Any actor can invest 10k or 20K to make BTC transacions fees high for weeks

I think this is a real problem for BTC is it ?