The long ones are long, sure. The short ones aren't....is that they are too long. We don't need "campaigns" that take us from level 2 to 11 or 13 or 20. Diversity of experience is important. I hope that in the not-6E era, shorter, more focused adventures come back into vogue and big adventure campaigns/APs disappear.
There's been a bunch of anthology collections of short adventures.
Tales from the Yawning Portal
Ghosts of Saltmarsh
Candlekeep Mysteries
Journeys Through the Radiant Citadel
That's about 50 short adventures right there.
Not to mention the various starter sets.