Help me out understanding the concept of tanking and how it is not something bad for a sport league

I see on Reddit, Twitter and YouTube people asking for Canucks to tank. Does that mean the league rewards teams to lose on purpose? What is stopping a mediocre team to play without a goalie just to tank?

I'm new to American leagues, but as far as I can tell, tanking is possible because there is no relegation. I had my doubts about the no relegation concept, but now I cannot understand how a system can make fans cheer for the team to lose.

That's not a good system from my point of view.

But again, I know this is common in American Leagues, and I'm new to watching them, so please explain to me as a newbie why the concept of tanking doesn't hurt the sport.