C’è qualche motivo linguistico per cui queste parole simili provenienti da lingue simili hanno significati molto diversi?

200 years ago, “šukat” also meant “to search” in Czech, just like in Polish.

Then, in Czech, its meaning underwent evolution. When you search a place, you move back and forth looking around. The “looking around” part gradually disappeared and it just meant “to move back and forth”. And finally someone noticed that your hips move back and forth when you fuck, hence it became one of the billion ways of saying “hide the salami”. All the original meanings died off eventually, the sex one stayed.

In Polish, none of this happened and it still just means “search”.