This is a tricky subject, imo, because even if Apple is just being money grubbing, there is a positive outlook on this. Finding reliable 3rd party parts for Apple products, even without Apple's meddling, is like cartwheeling through a mine field. My first post-university job was a lot of end user hardware support, and finding reliable parts that worked as advertised (for all brands) was a nightmare. Even previously reliable sites would switch inventory and suddenly get cheap knockoffs, which fit and looked like the real thing, but did absolutely nothing.
With iPhones in particular, this is horrible -- replacing a battery is a terrible experience just from a purchasing point of view. The actual process itself is not bad (and well documented by sites like ifixit), but you don't know about the issues until you have the part in hand and it sucks.
This is a mess for Apple since in a lot of places, third party shops do not care about the parts they order. They put in a replacement part as asked, and now the machine works even worse. As an individual, I'm willing to put out money to a company like ifixit to ensure I've got a working part and I have someone to point to when it doesn't work. For a lot of mom and pop shops that have margins to worry about, suddenly the part actually working isn't that big of a deal.
I don't want Apple to have this much power, to be clear. The right answer is instead to open up the official supply chain to third party resellers and drop the anti-competitive price fixing. But I do get their image concerns with regards to the third party ecosystem -- it's not Apple locking out third parties, it's third parties just making terrible products.