Bingo.
Fast travel remains a staple mechanic because game devs:
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Often can't figure out a way to make travel itself into a gameplay mechanic or experience that is varied and interesting.
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Keep designing checklists of things for the player to do, with games built around them, as opposed to inverse of that... which trains players to just be checklist checker offers.
There's no point to having an open world if it is not engaging or interesting, so... when your open world lacks depth, you end up in a nonsense situation where you have a poorly designed feature, with essentially a 'skip' mechanic for said feature.
... Why bother with the feature, at that point?
Hell, even the Rockstar games would give you interesting dialogue, in transit... not really gameplay per se, but it is generally engaging, can help with action intensity pacing, and of course, give you the story.
There are so many ways you could gameify or at least make travel itself more interesting.
Do that, and fast travel becomes near totally pointless.