Because they effect everybody, rather than certain classes. Also, everyone is pretty much on the same side with those issues. Everyone wants the economy to be doing well, not everyone wants abortion to be legal.
Everyone is very much not "on the same side" when it comes to climate change. Everyone wants the economy to be doing well, but the way to get there is one of the most controversial subjects there is. When even George Bush calls "supply side economics" "voodoo economics" and when half the opinions on the Fed are "abolish it" you can't call "the economy" an issue that everyone agrees on. Likewise, climate change. Sure - the majority of the polled public professes a belief in climate change. But the majority of voters (and lobbyist money) doesn't break down that way.