If you complain you will get told there's nothing that can be done. Even if you get sat in a seat soiled with vomit or poop[1][2]. And of course you may get bumped from your flight, potentially violently[3] or have it delayed, rerouted or cancelled.
So it's a market for lemons, you buy the cheapest ticket you can since the experience is likely to suck no matter what you do, and you try to endure it.
[1] https://www.washingtonpost.com/travel/2023/09/05/air-canada-... [2] https://www.newsweek.com/delta-passenger-forced-sit-seat-cov... [3] https://qz.com/954791/everything-that-went-wrong-in-uniteds-...