Howling:If The Doctor can go anywhere in time and space, then why does he always go to Earth in the 20th/21st century? Even when he is looking for a new companion?

I know there are out-of-universe reasons why The Doctor has mainly human companions and travels to Earth but he always boasts The Tardis can go anywhere in time and space. So why does it feel sometimes like the only places he goes is Earth in the 20th/21st centuries or Earth in particular. If he is going to stick with humans as companions for whatever reason, then at least go to another point in Earth's timeline, e.g. 14th century England or Earth in the 94th century. It just seems a simple and very easy contradiction to make and very easy to notice. I'm just a bit bored now of every companion (main companion) being from the same year in which they are introduced. That's why I like the comics as they can use aliens that are obviously not human like e.g. ice warriors or 12 feet robots. Although for some reason even alien companions are taken to Earth a lot. Think of Torlough. He was a Trion but went to Earth or was involved with humans quite a few times in his travels. It just seems stupid to think one species-humanity-is so important and influential when others seem to come and go as if they're nothing.