For me (considerably older than millenials) it's not choice fatigue or "default to bland and tested", it's "if I'm paying a small fortune for coffee / food[0], I do not want a crappy serving just because the barista/cook stubbed their toe / broke up / got bad news / etc. this morning and they're wildly off their game."

Starbucks, McDonalds, Papa Johns, etc. do not make "great" refreshments but they make them of a consistently sufficient level of quality that you can be sure you're not wasting your small fortune when you buy from them wherever you are.

[0] As, sadly, we are all forced to these days.