He did release the hitch, but in his setup, the load goes down to zero when the hitch moves "by itself" (not by the hydraulic pulling on it).
If you try to slide the hitch with your weight on it, the load is constant and that makes a big difference. Basically, when you makes the hitch slides, that means that you deform the hitch's shape and put some play in it. It becomes less tight and slips. But if the load is still here, it tends to eat the introduced play, part of it at least, and tighten the hitch further more. So, at the next attempt to slide the hitch, you try to deform again the shape but, one, it needs more force to do so, two, the tighter shape allows less play when deformed. Finally, the hitch needs more and more force to slip and doesn't move as much, if at all. You just get deadly stuck. All you can do is take your weight off of the rope, work the hitch to release the cinching force by putting some slack in it again, akka, you reset the hitch's shape.
Plus, you definitively can't climb pratically if you have to put so much force than he did on his hitch.
On average, the sweet spot to keep an hitch working (grabing and releasing at will) is around half your weight. Actually, you fine tune it for a good match.
That's the main problem if you want to go srt with this setup : too much force on it to go back and forth. You can make it slides one time or two, but that's it, locked hard. Hence the development of the alternative solutions by our fellow genious climbers : adding more friction into the system to take part of the load off the hitch and makes it works again. Et voila, there are the HitchHiker and the Ropewrench. Added benefit, the suplement fricton is self adaptative to the load and allows a much wider range of workload. Genious as I said.