When I complained to my friend at Instagram about this, this is the exact answer she gave as to why they have it like this.

Instagram is a Duke of dark pattern ux, I'd say king but there's travel booking websites out there that hold the crown.

It's also there to force the user to watch the full video to see if the build up to some final product was actually worth seeing. Both reasons are there to take seconds off your life to juice their engagement stats.

Given that Youtube copied it for their "shorts" clone of TikTok/Reels, it must be working for the platforms...

I think their reasoning is that if it’s just a few seconds it “simplifies” the UI, which is why if the reel is just a bit longer it is trackable.

TikTok on the other hand I think the video needs to be much longer to be trackable.

YouTube shorts are seekable.

It’s a double edged sword, because the seekability of YT Shorts mean I’ll actually watch them.

That is a relatively recent change.

Huh, yeah, I just checked and can indeed now scrub them! It's been a while since I last gave them a chance.

Not in my web browser right at this minute. I have to edit the URL from /shorts/ to /watch?v= all the time.

I used a greasemonkey script to automatically edit the URL for me

Really wish the engineers behind that design did us a solid and at least left the shortcut keys (left/right/j/l) in. Dropping those too is criminal.

You definitely can jump in a video (at least on android).

The white bar at the bottom, which shows the progress of the reel/video, can be dragged. It is a very buggy experience, but it works.

I think it doesn't work with very short videos.