I mean, my feeling is usually kind of the reverse, maybe I'm a neophiliac or whatever but if a game is like, absolutely in my "strike zone" interests-wise, i.e. it's very similar to a game I like in terms of subject matter, then that automatically makes me more interested in it, not less.
To a point, I'm the same way. I'm more interested in a Trek Like than a novel science fiction setting. I was excited for 2d20 STA when it released. I've run a bunch (a couple campaign-years of almost weekly sessions) of STA, and I like it. I like how it makes it easier to get my players to think in terms of drama, and how it added nifty mechanics that other trek games would benefit from a similar bit. It does, however, have a couple big issues... ship combat being the big one.
What would make me less interested isn't "It's about that subject you like running RPGs about!", but rather "The rules are rather similar to that RPG about that subject that you already have!" or "This game just applies generic-ass rules to the subject".
Very similar - if it's adaptation of the rules, and I like the setting and find the ruleset tolerable, I'll be delighted to read it... until, at least, I find bits that make me go "Ugh!"
Hence yet another d20-based, level-based, linear-power-gain Heroic Fantasy RPG doesn't necessarily make me go "Ooooh!", but a gain using very different mechanical approaches and ideas to explore Heroic Fantasy or a similar area does make me pay attention.
Which is why I'm interested more in Daggerheart than (whatever name Black Flag changed into). The latter set out to be more D&D-5E-ish... while Daggerheart aims for a similar range of settings, but a different playstyle and GMing style, and mechanicalizes those differences.
I don't think this is uncommon either - like, there's a whole bunch of Cthulhu mythos games for a reason, and I don't think it's just a lot of people thinking "CoC sux lol" or something, but rather because people like seeing different ways it could be done, and like trying new games with similar subject matter to see if they prefer them.
And trying is part of it because like, how does one know that, say Arkham Horror and Candela Obscura won't do a better job than CoC? I'm not saying they will, but I'm making the point that most people don't just know that - that wanting to find that out by playing them or at least reading them is actually very common.
But only common once one's gotten them outside the D&D/Pathfinder
trap zone.
Certain 5E variant engines seem to be excellent at that, save for their specific settings. (I'm thinking mostly of Pugmire, Monarchies of Mau, and Squeaks in the Deep - the PugSteady System games... with a more pick your path of growth system for it's classes...)
I'll note as well: many of my friends who like the Cthulhu mythos don't like BRP at all. A few do, and love BRP and CoC. It's a bit of a divide... Many times, I've seen them try a new system as a group compromise... And that divide also prevented me from running ElfQuest, RuneQuest, Worlds Beyond, and FASA Trek.