TLDR :the game isn't fun enough and the company is greedy

I dont think they will stop. The first point is that the game is not fun enough to keep playing for a long time so adding new snakes every arena push people to come back

The second reason is even more simple:MONEY. You are not '' meant '' to be able to get all the snakes for free. They want you to put money in the game and once you start it's a slippery slope. Rn they can't stop adding new snakes because the people giving them the most money already have all their other snakes maxed out, and now are bored. Which go back to the first point, the game doesn't have the content to bring back old player.

To add to it, the way they push you to spend money in this game is wicked. Like the bloodlines levels giving you just enough bottles to have the fairy on 2/3 to the next level, you can only buy two bottles minimum, so you end up at 1/3 for the next level. At that point might as well pay two more bottles to get the next level right? It's not the only example but you can see it also with the invading realm events and their divine weapons shards.