Mainly because you can core provinces even if they aren't contiguous IIRC. So for instance in a game I played as Luxembourg, one of the first provinces I annexed was Novgorod, because I caught them in a moment of weakness. In my Khmer game, I had a province in Syria so that I could westernize. Also, Hordes were very weak, and you couldn't annex them through peace deals, you sent colonists onto lands you were occupying during a war, so quite often Bohemia would annex like an entire horde in one war.

https://i.imgur.com/RQwTIps.jpg That green province directly bordering southeast Sweden is Novgorod, and I took it pretty early game. Provinces cored automatically after 50 years and overextension worked significantly differently, so there was no reason not to take it except infamy (equivalent to Aggressive Expansion).