If you can already swim fast in water then you only need to panickingly point yourself straight at the surface as you flee predators to find yourself momentarily airborne whereas if you’re a land based creature getting and staying off the ground becomes more likely the higher your jumping off point though but so’s the degree to which you’ll go splat.

In which case maybe the first creatures to colonise the land didn’t crawl out the sea but accidentally landed there after terrific salmon like leaps and because they’d already been learning to handle longer and longer periods out of water some of them were able to survive long enough to get back in the sea.