The St. Louis Blues have been free to spend up to the salary cap ever since Tom Stillman and his partners took over the franchise. However, while the team has spent a good amount, they always left themselves some sort of leeway, even if it was a small amount.
In 2019-20, partly due to raises from winning a Stanley Cup, the Blues did not have that leeway. They were right up against the cap ceiling and had to rely on long term injury relief in a couple situations to keep themselves compliant.
That bloated salary pool has kept them at the top of the Western Conference.