I assumed the opposite because I haven't heard about GTA's story in ages, but could be a sampling bias. It's hand-wavy, but last I recall most of the microtransactions didn't show up in single player (like if you bought a car, you couldn't use it in single player) so the people spending money on it are doing it for online, not the story.

I didn't think the story was earth-shattering; it was fine, but no Baldur's Gate.

Edit: In retrospect, the characters were fairly iconic. I still distinctly remember Trevor.