[jjallen]

To support this: Oceans are more conducive to exploration due to their natural currents and lack of mountainous regions or rivers which inhibit movement.

Like the comment below was getting at: if you are water bound, you are very unlikely to discover or become proficient with fire, which to us, as if now seems like a requirement to travel through space.

There’s also the massive weight disadvantage water has compared to “air”.

So no fire and have to travel with a water filled rocket instead.

But again maybe these are just land centered views.

Maybe you can just inject oxygen into the water that merely surrounds your head.

And maybe there’s a hydrogen power rocket that is more efficient than our fire ones.

[RandomBacon]

For traditional rockets, it's not so much fire, as it is the rapid expansion of matter and the force that it generates. Fire just happens to be the most convenient method for us.

There could be metals under an ocean that could be mined. An underwater civilization could potentially harness nuclear power.

[lwo32k]

Volcanoes can launch things into space. There are already systems that try to tap into it. So its possible in theory to trigger it underwater.