They are aware of the risk of career-ending injury on the pitch already and can make an informed decision about whether to play the game but if you start cutting their salaries that risk becomes relevant too. They have to be given a fair deal to get bashed about in RL.
With post-covid complications there are many unknowns. Lots of people who contracted the disease back in March/April are still suffering with 'long tail' symptoms - shortness of breath from mildly strenuous everyday activity, heart arrhythmia, severe muscle pains. I was listening to an NFL podcast the other day with some doctors that work with NFL clubs about the protocols they are developing for a return, and they have a lot of concerns. Basically they said the average public thinks that as these guys are super fit athletes, they will only get mild cases at best, which isn't guaranteed but also they have concerns because its a blood borne disease, affects multiple organs and causes the blood to clot - this can happen even to people that have mild symptoms in the first case. They are worried that players who appear to have recovered and are superficially healthy will still have some underlying effects going on which could be dangerous if they are taking multiple hits to organs, and that it may increase their risk of sudden cardiac events during strenuous activity. They are looking at things like advising some players not to play in away games at Denver at high altitude, if they have had covid. With all these things they just don't know what will happen but there are medical reasons to believe there are risks so they said we're basically rolling the dice and seeing what will happen.
The players are stepping into the unknown and taking risks so that the game can get open again. I'm sure most of them are willing to do that, but they are entitled to a fair deal in return, if they aren't getting that, they are entitled to say no and we shouldn't let whatever propaganda the league puts out in that situation turn fans against the players.