What this discussion shows is what you would expect with any market. When a company gets something very right that makes them a success, they are held to a higher standard and attacked.
iRacing is the 800 lb gorilla in the online racing community specifically because they have a solid business model that allows regular competition that they have been evolving and growing over the past decade. This is not all the result of their marketing engine. The reason people stick with iRacing is the competition they provide. They have critical mass which gives them sustainability and consistency.
My take is that they get so much right that it really frustrates people when there is something they that leaves room for improvement.
As a result of iRacing's success, people want to see a competitor step up to the plate to challenge them and be less expensive. Some people were hoping ACC would be that competitor with a real online racing system, but they don't have a system that appears to work well and they don't have critical mass and rather than building on AC which people liked, they created something all new that doesn't seem to perform as well. I'm not saying that they didn't make other improvements to the game, just that there has been disappointment with their online racing capabilities.
I've read many complaints from people about how PC1 was still buggy when it was discontinued and PC2 was just starting to get good when they started talking about PC Revolution. People feel abandoned and want them to continue developing what is already out there.
In both cases the base of players is fragmented. People don't want what they have to be left to rot and to then have to buy a brand new version that they know will be buggy and take a while to get worked out only to get drop kicked to the curb when the manufacturer feels the need to come out with something all new so they can generate revenue.
Each product cycle is being driven by a different business model. Most racing software titles have to come out with something new and shiny on a frequent basis to stay in business and every time they do, they leave some of their players behind, or make them evaluate whether they want to try something different. People end up with a copy of AC and rfactor2 or r3e or PC2 etc..
iRacing gets a lot of things very right, but they aren't perfect. Because they are the big dog some people expect them to be perfect or to be the best at everything.
The critical thing iRacing does have is a very solid core with constant evolution. They will not ever be the best at everything, but they will provide solid competition and continue to improve things and not leave you stranded. That is why they will continue to grow while other sims feel the need to completely reinvent themselves every few years with something 200% better than the last version