Probably because simple electromagnetic locks use quite a bit of power continuously, and nobody with enough experience was involved to know that low-power electromagnetic latches and pin pullers exist.

  OceanGate CEO Stockton Rush hired interns to design the Titan submersible's electrical system: Report

https://m.timesofindia.com/etimes/trending/oceangate-ceo-sto...

This is not energy efficient.

A better way would haven been to have mechanical latches, that are connected to the weights and which use the battery to unlatch the locks.

I am curious how the weights are wired, because you cant just run wires from inside the sub to outside. The pressure gradient is too high. So with mechanical cables holding the weights.

I think they didn't do that because they would need to have that system independent of the system inside the submarine or otherwise they would need to drill holes in the main hull to provide power for that. Given the fact that the aystem was controlled by a cheap controller pretty sure they didn't spend that much money on the weight drop system either.

Maybe it's just a good idea that didn't occur to them? (Not being snarky, I'm curious too.)

Related: Is there a way to design an electromagnetic coupling that only uses significant power when it needs to work hard to maintain the connection? Because otherwise I could see battery drain being an issue.

Well, as the article explained. There was a non-battery backup.

> “We had special weights on the submersible that will dissolve after 24 hours so they will just drop off and then we would be able to get back to the surface.”