One of the biggest impediments to the success of other games is that game stores (at least here in the States) largely treat RPGs as zero sum. It's really the combined stranglehold of D&D and Pathfinder since the 4e era that is the issue. You're lucky if there's even anything on the rack that does not come from Wizards or Paizo. In the 5e era Adventurer's League has made this worse because it is a format game stores can promote in the same way they promote Friday Night Magic. Home games and especially running other games at the store are often discouraged. I have pretty much given up on game stores as a way to connect with other gamers or recruit for not 5e / not PF2 games.
Over and above availability (and this is not my saying you're wrong), its easy to underestimate how much weight the network factor has in some areas.
Let's say you have a fellow who is, for whatever reason, dissatisfied with D&D. It doesn't even matter why. So what are the steps he has to take to play something else?
1. He has to be aware of it. While that may seem stupid in the day of the Net, I've encountered people even in recent years who were, at best, only vaguely aware other games existed, some for the reason you reference above, some because they didn't actually buy game books themselves but just used other people's. This is particularly easy to do in small communities where there's no local game store and what gaming population exists is pretty much D&D universal.
2. He has to figure out what he wants instead. Even once he finds sources to talk about other games, it can well be overwhelming. Does he even want to stay within fantasy? Even within there, just to look at the more well known cases you have Warhammer, RQ, and various PbtA options, and I'm forgetting some common cases because its early and I didn't get enough sleep.
3. Now that he's figured out what he wants, how does he get to play it? Does he GM? If not, he's got a serious uphill battle to fight because he has to get others to engage with the game, including
someone else to run it.
Given a fair amount of the gaming populace is pretty casual in their approach to the hobby, is it any surprise that this most likely means the majority of people, even people who find elements of D&D annoying, are just going to stick with what's already at hand?
(And of course there's the issue even in bigger places that most game systems do not have anything like D&D's organized play system; the only other one I know of that does anything like it is (surprise) Paizo).
By the way what Wizards has been able to accomplish with both Friday Night Magic and Adventurers' League is some damn brilliant marketing. They have basically turned gaming stores into a vestigial marketing wing that pushes their products, keeps players engaged, and builds community around their games. It also has a chilling effect on anyone trying to compete with them directly.
Or, this.