Why are we not funding this?

Because it's expensive?

Something to do with ecosystems?

And it could kill a lot of fish life

It'll interfere with ocean currents' natural behavior?
Kinda expensive to attach to the sea floor when its behavior is kinda unpredictable?

There's something quite similar to this already in effect, actually. There are turbines set up underwater in locations with large amount of tidal activity (as opposed to currents) that are turned by said tidal activity, which are used to harness the energy. It's a great source because it's sustainable, unless the oceans decide to just not do what they've done for millions of years. Just a little fun fact :)

There's still a few technical hurdles of durability to get past. It's a lot harder to repair them than wind turbines.

The density of water should be taken into account, since the turbines would need to be supported much more and the propeller part would need to be smaller.

I see that the science side of fs have arisen

slicing whales in half

People dont realise that with some "great ideas" there are some massive drawbacks that outweigh the benefits

because nuclear (specifically thorium) is superior in every way

Because people are usually idiots and no one important/rich listens to people with ideas?