Ancient-Red-Dragon: GOG is definitely an obscure store.
They even openly admit it themselves, albeit in PR-speak language, when they say stuff like they think of themselves as if they are akin to a small boutique store.
Someone posted the monetary value of Steam vs. GOG before, and GOG is like a very very very tiny drop in the vast ocean that is Steam. There is no reasonable comparison at all.
I guess you are right. When i go on Reddit (a mostly American site, so probably biased towards Valve) many people jsut simply assume that if you are playing a PC game, you must have got it from Steam... Even if it's availaible on GOG and Epic and the publisher's own site, or a combination of those...
However i don't know whether it's enough to consider it obscure. I mean Harry Potter has probably outsold Narnia a dozen times over, but that doesn't mean Narnia is obscure.
I am guessing there are many people who know about GOG but don't spend much money here since the games they play are FIFA, CSGO, DOTA, Battlefield, etc. and they can't get them here.