Tanking is not one in a choice of strategies, it is the supreme strategy.
More and more teams tank, now several teams in the same league tank. Why should it stop ? More and more teams in a league may tank, at least part of the season, except those going for the title. Why would you keep a roster to win half of your games by 100+ ? If there are many teams tanking, you can always save yourself later in the season. It makes sense strategically, how can you guarantee this will not happen, half the league tanking ? Would it make an interesting game ?
Some want to see the game from an individual perspective only, tanking is a choice that one makes to beat the others. They completely disregard that a few tanking teams in a league ruins it, the whole season and the appeal for the game. Devs might want to take this into account.
And very importantly, the same teams in top leagues you are talking about, many have gone broke and are saving their asses with tanking. They have/had an ageing roster worth peanuts, they would have gone down, tanking is their life-belt. Tanking is not promoting the renewal of top teams.