Some people saying they wouldn’t like it is not remotely the same as “no one would like it.” And thank God, or else my game wouldn’t have sold at all.
The Greek-derived terms with which I peppered Choice of Rebels aren’t a conlang, but they’re similarly unintelligible to plenty of readers. I’ve had no shortage of bad reviews like: “A tad boring. The language uses many new made up words which describe things, which you keep on having to lookup for reference, interrupting the flow of reading it.” (Currently one of the top four reviews I see when I open up the Play Store).
But of course that’s not the whole story. Plenty of people bought it and liked it (many no doubt despite the gameworld having its own distinctive vocabulary, but that’s fine). It’s been a success even though lots of people didn’t like my authorial choices.
Like you, Tolkien started with the conlangs (which as an aside is a good reason he didn’t have even more elf races–developing a new dialect for each one would have eaten his whole life). His story wasn’t about the languages, but featured them heavily. That was his passion.
No doubt that cost him some readers from his day to this. And I don’t think they’re why LotR was popular. Most of his fans would surely have enjoyed LotR just as much if Quenya and Sindarin were gibberish with a few snippets of sense (“dor” means “land of”!) rather than fully realized languages.
So yeah, don’t add a conlang as a measure to make your game popular. But if you love conlangs, don’t be afraid to include one just because some readers won’t like it. “Some readers” will dislike any creative choice you make.
If you want to find a big audience, try to leaven the potentially unpopular stuff you include for your own satisfaction with other more broadly popular elements. (Like Tolkien did, by mashing up his professorial passion for languages and Beowulfian myths with the bedtime stories he told his kids.) But make sure it’s all stuff you enjoy, as Tolkien certainly enjoyed hobbits and Bombadil. If you’re writing solely for the tastes of an imagined audience rather than your own tastes, you’re likely to be doubly disappointed–you won’t enjoy what you’ve written, and there’s a good chance that others won’t either.