Space is hard to get to, no gravity, and there's radiation.
Underwater has high pressure, corrosion, and no natural lighting.
When you get an air leak in space, you find the hole and patch it. When you get a leak underwater, you don't have to worry about it at all because it takes care of things in microseconds.
In 2025, People Will Try Living in This Underwater Habitat (spectrum.ieee.org)
Self-Driving Waymo Cab Smashes Into Delivery Robot (futurism.com)