But those ships are not like planes, you can't reuse them multiple times a day, the trip to Mars takes something like 6 months, and that's a launch window that opens only once every 2 years, the rest of the time it takes longer and more propellant, so your ships would make the round trip in 1 or 2 years, so you'd need to build 820k to 1.6 million ships only to be able to shuttle the population to Mars and stay constant on Earth.
That would be a serious industrial investment. A quick search says that there are around 24000 planes in service in the world, and over the course of history, 150000 planes have been built, including all military and commercial aircraft. So we'd need to build a production with many many times more capacity that all the airplane builder that exist today.
Then there is the energy cost of those ships, Earth gravity well is actually pretty deep and chemical propulsion only just is able to escape it. That many launches is going to need a lot of energy, a rocket can hold up to 500 tons of fuel, multiplied by several thousands of launches per day, and you reach a non-negligible percentage of the current daily worldwide energy expenditure.
The idea of being able to mine asteroids or outsource production in a meaningful way on another planet is similarly unrealistic, escaping gravity is not easy. Of course the technology will improve, but not by the several orders of magnitude that would be needed. When we colonize space, it is likely that it will be more like seeds, with only relatively minimal exchanges when the scale reaches a whole planet.
