The original reasons for the players unions were because of pay, unironically, because even certain stars used to have to work during the offseason because of not making enough. In fact, the MLB All-Star game was originally designed to be a scheme to help those All-Stars get more money for their retirement, while the owners just took everything. Considering how sports are how a lot of people still get out of poverty, and most teams are owned by billionaires who wouldn't spit on us to stop a fire, I don't hate that traditional athletes have unions, I hate that esports players don't have unions, because of not taking heed of what happened back in the day.

Also, the entire reason "free agency" exists is because of lawsuits, because teams used to be able to just extend you until they wanted to get rid of you, you had no choice as to what team you wanted to play for.

In MLB specifically, the reason that players want to at least play for ten years is because that's when they're guaranteed a full retirement, as while yes, the stars get paid huge amounts of money, the non-stars are still in the steepest tax bracket.

Team owners being pieces of shit is why players' unions exist.

Edit: https://www.mlbplayers.com/history

https://nflpa.com/about/history

https://nbpa.com/about

I used to think player unions were unnecessary too, until I learned just how terrible owners were, and a lot of them, still are.