To maintain Minecraft's lucrativeness, its relevancy needs to be maintained. The only way to maintain this relevancy is if it continues to improve with updates, and continues to feel fresh.

Naturally, when things slow down, or if things feel like they aren't coming, people will move on. This has nothing to do with the complaining, and it has nothing to do with entitlement. It's the nature of interest. Losing interest in something cannot be helped, and it happens at different times for different people.

Eventually, if the api does not come, and if updates continue to slow down to a crawl, people will leave. It's just the way it is.

You cannot be a part of a community with such vitality, and be part of a game for so long, and expect people not to be concerned for the future of it, and to not get nervous about their own disinterest creeping up behind them as time goes on.

Just because people have gotten their money's worth in your eyes, and just because MC updates are free, does not mean it is above criticism. People may have not put a lot of money into the game, but they have put a LOT of time into it. Like I said above, relevancy is the foundation that has held it up this long. Without these people, MC would have crumbled a long time ago. So in my eyes, they have every right to complain. I would rather hear an opinion from someone I disagreed with than hear an opinion I did, laced with venom.

Where people got this notion that this is not a give/take relationship is beyond me. Mojang does not update the game out of the goodness of their hearts (even though I do believe they have goodness in their hearts). That's just a naive. Mojang is a company first and foremost. Merchandise, and other peripheral, money pipes stay flowing as long as MC stay flowing. The developers "work" on MC. Work is the key word here, and they do not do it for free.

tl;dr Complaining is a part of life.