Cost certainly doesn't hurt. You can some very decent ukes for around $90... any guitar you get in that price range is going to be worse than garbage.

I dunno. I'm nothing special when it comes to guitar but my first was a $50 pawnshop special that worked well enough. Then my second (this time an electric) was a crappy Strat knockoff, also used, for $150. Nowadays you can even get them cheaper from Walmart-type brands like First Act or online from importers like Rondo Music.

Sure, they're nothing great but they work for learning to play and screwing around with your friends in the basement or around a campfire (which is probably all you'd be doing with a uke as well if you're a beginner).

Keyword: USED.

The $90 Ukes I'm talking about are brand new.

There was a major Ukulele boom during the great recession. A lot of people found themselves out of work and needed a way to fill their time, and as you say they are inexpensive compared to a guitar.

Definitely a bit of a college trend, but it's certainly been in multiple pop songs in the past couple years