I just made a comment in another thread that Cape York, a huge chunk of northern Queensland has a mere 18,000 inhabitants. It's more sparsely occupied than northern Alaska by nearly a factor of two.

Why? Because it is low-value land due to monsoons turning the dirt into mud, and that dirt doesn't have enough minerals in it so agriculture is too difficult to bother with.

It has free oxygen. It has 1g gravity. You can fly there for about a thousand dollars instead of a thousand billion. The radiation might give you skin cancer, but won't kill you immediately. There's too much water. It has animals you can hunt and eat. Etc, etc...

Practically nobody wants to live there that wasn't already there for generations.

If the human race can't be bothered occupying land like that, then colonising Mars is so, so far down the list it isn't even on the same page, book, or library shelf.