If they don't start serious habitat development until Starship is ready, then, Starhip will be decades old by the time anybody is ready to make a Mars colony. Besides the structure of the habitats themselves, there a ton of technology that would need to be developed first. Life support equipment and systems, space suits, vehicles, any sort of plan to produce food. Nobody is seriously developing this stuff, you have a few million dollars here and there thrown at university projects but no serious investment. It would take a Manhattan Project sized commitment, but who would pay for that? Not Elon Musk, he says that he assumes other people will. There's no money in Mars colonization, it's a pipe dream for young dreamers.
> To add to that, it arguably doesn't make sense to develop habitats at all unless something similar to Starship is flying.
It doesn't make sense developing Starship unless you have paying customers lined up. Launching satellite constellations is a market that actually exists, Mars colonization doesn't and won't for decades at least, by which time Starship will likely be obsolete anyway.
Furthermore, you're ignoring the part where Starship isn't a Mars rocket and doesn't even resemble a Mars rocket. If Elon Musk had never spoken of Mars, there would be zero reason to suspect that Starship was meant to be a Mars rocket. His words alone are the basis for this belief. How much are his words actually worth to you?