People knock MK9's balance a lot, and I agree it was imba, but I mained Scorp/Sub in that game and in even in match-ups that were not in my favor whatsoever, I rarely felt like I lost a game or set due to wrong guesses, but to wrong decisions. If that makes sense...
Hell, even in a Sub vs. Cyrax match, there was at least a chance to win if you played your hand right and played it patiently. And it was at least rewarding to outplay those match-ups and hype as hell to watch others pull it off too. In MKX, 'outplaying' just tends to feel as if I made the right choice between going for my overhead or low starter... not exactly rewarding.
Balance issues aside, the game was just damn fun, it was crack and it brought me into competitive fighting games. In MK9, win or loss, I was having fun. I don't find it hard to believe that there's people who definitely like MKX, but I feel few people LOVE the game. I have this nagging feeling that everyone who plays the game competitively/defends it wishes it was more than it is (could just be me projecting my own feelings), and that could be for a number of reasons already stated, such as the absence of notable personalities from the MK9 days.
I remember on an episode of KTP back in MK9 when 16 Bit and the guys were discussing what they wanted to see out of a sequel to MK9, and 16 Bit said he basically wanted as little change as possible from MK9. I took that as him saying he wanted a sequel that felt familiar with better balance. Well, MKX to me feels very different from MK9, and that may be a good or bad thing depending on you ask.
-edit-
I also want to point out, notable NRS/MK9 players such as Slips go on about how much of an improvement MKX is, yet we've seen less of them competitively (if at all) than we did in MK9, the supposedly inferior game. I understand that life gets in the way, and we don't always have the funds to travel, but to the "old school" MK9 players (the ones not already in YOMI) that truly feel this is the better game, where the hell are you? There's so many missing faces for this supposedly superior game, and even the ones that are familiar, in some cases, just don't seem to have the same spirit or come off as very inspired. Brady, for example, with all the supposed issues that Sub had in MK9, seemed way more passionate and inspired to compete back in those days. PL doesn't come off as someone who is 'into' the game that much either. CD Bros. are missing, etc. I could go on.