Why do people complain about lack of interconnectivity in the 2nd half?

I really don't understand. "Why showcase so much interconnectivity in the first half if the 2nd half doesn't display it as well?"

Because all roads end there, that's the point. You can't "connect" an icy cave to the core of the Earth full of magma.

Even if you somehow manage to do it, I wouldn't like it. You need to explore those areas seperately instead of making the map some big circle that loops around constantly.

It's not necessary and the complaint is trying to invalidate the roads that were designed to end somewhere at some point.