It's not actually, look up some photos of the sun setting over the ocean. Here's an example:
https://stockcake.com/i/sunset-over-ocean_1317824_81961
That’s only if the sun is above the horizon entirely.
No, it's not.
https://stockcake.com/i/serene-ocean-sunset_1152191_440307
Yes, it is. In that photo the sun is clearly above the horizon, the bottom half is just obscured by clouds.