Why does everyone want Chemist as a new job?

[GucciSan]

I feel like you would really have to go out of your way to never see the Geomancer side content in the game.

And while you do have a point about the MSQ, I still feel it would be odd to have such a staple mentioned and put in for 3 years to have it be nothing.

Not necessarily; The AST quests give a great deal of GEO lore themselves but not everyone plays AST or even healers.

I don't mean to be dismissive of GEO altogether, just that between the two Chemist seems like biggest clue to a potential Job despite all the lore GEO has now because it was featured in the MSQ where GEO really isn't. IIRC the only MSQ related instance that every player would have experienced GEO related content is Swallow's Compass and while you can get an idea of what Geomancy is in the world of XIV it only goes so far because they're only dungeon enemies; it's no more than the enemies of the 5.3 dungeon providing lore on their own takes of the current Jobs.
The team have to accommodate for the lowest common denominator by assuming people haven't done side content and excluding it from their clues, so the GEO quests that expand the lore feel more like world building, where the Riki-Tio segment could be summed up as:

"I wanna be a Warrior of Light! One that fights with potions!"

"A Warrior of Light that fights with potions? That sounds crazy, but it just might work! And we work hard enough one day there will be potion wielding WoL everywhere!"