My company countered my external offer. Everyone says never take the counter — why?

Got an offer elsewhere for about 20% more. Told my manager I was leaving, and within two days they came back matching it and then some, plus a title bump.

The internet is weirdly unanimous that taking a counteroffer is a trap: you'll be seen as a flight risk, the reasons you looked in the first place won't change, most people who accept are gone within a year anyway. Part of me thinks that's just cynicism. I like my team. The new place is a total unknown.

Has anyone here taken a counter and been glad they did? I'd love to hear from someone it worked out for, because right now all I've got is the internet's blanket "don't."