Around twenty years ago, as a teenager, I was building decks for Magic: the Gathering pro tours, and proudly reached #1 in the world in constructed rank and #3 in the world in limited rank on Magic: the Gathering Online.
So that's world number 1 in M:tG Online. From experience, M:tG Online is (was?) a less competitive game than the physical-cardboard game and I'm not even sure that even in the cardboard game DCI rankings (the "rank" in the article) is exactly correlated with being one of the top players at sanctioned tournaments, like Pro-Tours and World Championships, or their qualifying events. I think it's possible, oddly enough, to have a high rank in DCI points without being a pro. For example I seem to remember Friday Night Magic tournaments conferring DCI points for wins (and taking them away for losses). But it seems the whole system has been discontinued by Wizards of the Coast so I can't easily check how it works anymore (or check my own rank...).
I don't think it's a problem at all that you didn't enjoy it after A2. Some folks do (like Jorbs or your comment's parent) and some don't.
If your line of questioning was more along the lines of why it didn't wear off, I can give my own anecdote. I found that the increase of difficulty makes the game more interesting to think about because you have to be much more methodical in how you craft your deck and play it. There are a lot of variables to manage and account for too.
I feel like after 12 or so hours of chess I'd figure out how to not hang pieces. From there, how to find the best moves is just a question of dedicating energy into finding them in game.
I'm not sure why anyone plays more than 100 or so hours of chess. Doesn't it get boring?
Don’t get me wrong. I’m impressed with people doing it, but I don’t think I can.