Same answer as to why the Raiders and the Athletics left Oakland to build new stadiums in Vegas while the Red Sox still play in a stadium that is over a century old.

The team owners, by and large, care more about money than they do about the fans of the team, and flashy new stadiums get butts in seats at premium prices, even if the team itself sucks ass.

The only way MSG gets replaced at a site remotely similar to what it has now is to take over the second part of the Hudson Yards project, which would require a lot of stakeholders to agree on the move. Outside of that, MSG would likely need to move to an outer borough or New Jersey, something that the Knicks and Rangers don’t want to do. So, the Knicks and the Rangers play in a very old stadium.

For most North American sports team owners, they generally want a newer stadium as a draw. I guess Calgary has the room for a new stadium in a place the owners are happy for it to go.

Because they put $1B into refurbishing MSG ~15 years ago