Yeah, that's a good question. And you are right about it being too large. That's definitely a concern. I have a 30lb lift bag. I didn't want it to be too large for the reason you mentioned, plus they can be tougher to manage. I have no doubt that the 30lb bag would not have been able to fully lift the latest anchor all the way to the surface. It likely would have gotten the anchor and some of the chain off the bottom.
It would, however make it 30 lbs lighter. That can be huge both for the diver or the people on the boat. I have a windlass on my boat as I do not like to manually bring up any anchor if I can avoid it. I wouldn't be able to use the windlass as it needs a specific size rode and chain, plus it's occupied. But reducing the weight could be huge for either diver or topside retrieval.
I see them fairly regularly. I've been asked to unhook one for a fishing boat in the past. The anchor I lost was actually one that I retrieved. Me and a buddy actually retrieved two in one dive trip. The smaller one went on my boat. The large one was too big and I ended up selling it. It was at least a 35lb plow anchor (may have been 44lb), so for 35'-52' boats or for 40'-58'. I ended up selling that one for a couple hundred.
Retrieval of that one was a bit strange. Anchor was hung up on artificial reef structure in about 35' of water. Anchor was connected to chain and rode. Rode was cleanly cut and not down there for too long. So, we freed it up so that nothing was hung up and began our ascent. My buddy held on to the rode. Unfortunately it stopped about 10' below the surface. So he held onto it for a bit and I grabbed a line from the boat, hooked it to a fender to keep it at the surface and dropped the rest to my buddy who tied it off. We then pulled it up from the boat. We get maybe 2' tidal swings around here, so the rode being 10' short but cleanly cut didn't make sense.