First of all, the NHL is providing raises. The cap is probably going up by $1m and will go up by $1m per year every year until the debt is paid off, at which point the cap will again be based entirely on the 50-50 split.
Second, other industries don't have the fixed tie between salary and revenue, although a couple of the other sports do. Tied into that... just a quick look at baseball. Baseball players took a paycut for the 2020 season based on the number of games played. Their salaries were pro-rated. NHL players were not willing to do that, so they got paid their full paychecks for the 20-21 season despite it only being 56 games long. So, the combination of the full paychecks, the hard 50-50 split, and the loss of gate revenue means the players owe the owners money. They *knew* they were going to, because that's how the CBA was laid out.
Third, the other leagues aren't quite so gate driven because of their TV contracts. The NHL just signed nice, big new TV contracts so they should be more insulated better from this kind of thing in the future.