Starting a colony on the ocean floor is also challenging and possibly leading to a lot of innovations [1]. However, compared to the efforts around Mars, there is no-one trying to settle the deep seas (that I know of). You don't need to go to another planet to find problems.

So for Mars, I don't think merely the opportunities for _any_ innovation, are a convincing enough argument, at least for those investing in Mars. For them the specific innovations around spaceflight and non-earth construction are indeed valuable, because of future expansions into space and first mover benefits, using Mars as a stepping stone.

As for the colony on Mars itself, I speculate that having somewhere outside of existing jurisdictions is also attractive for a lot of people; the new unclaimed West. Some may imagine this to become a scientist utopia, free from the restraining politics of Earth; others might be more cynical.

We will see.

[1] https://www.bbc.com/future/article/20130930-can-we-build-und...