[Flux]

When we watch the last scene with Tennant's doctor with Donna's family and she says to him he doesn't have to stay, and he replies we will see. So we all know the doctor would get bored, he actually got bored already by taking Rose to Mars on a trip. So this can easily explain his absence when London or the UK or indeed the world is in danger.

Isn’t it just as bad if he pops off to Mars because he’s bored and doesn’t bother returning even when his own family are in trouble?! He’d deserve the slap Sylvia gave him when he returned!

In all seriousness though, I know there are plenty of ways to explain his absence. What I find perplexing is why RTD would create the need to explain it in the first place. There was no reason to have 14 settle in 2023. There were many other ways to give his story the same full stop without creating the issue. It just seems uncharacteristically sloppy for RTS as a writer, and even if they choose to ignore it going forward it still leaves an awkward loose end for any earth-based stories in the main show or future spinoffs based on present day earth.