I sort of eased away from watching the show during the Tennant years, because every plot seemed to be a human one; the Doctor didn’t seem to actually go anywhere other than Earth, and it was getting redundant. And it seemed to me when I watched and loved the show back during the Baker/Davidson years, that alien worlds were much more common than they were on the new show.
I wonder if audience expectations play a role in that. In the old days, you could make an alien world by building a couple of strange sets, maybe create a miniature for some effects shots, and give everyone a funky costume. That wouldn’t fly nowadays; we’ve come to expect sweeping CGI vistas, and that’s just not feasible to do every week.