Please note that the ISS was assembled on orbit from many small components and subassemblies: the largest module was IIRC about 22 tonnes, while the ISS itself

Please note that the ISS was assembled on orbit from many small components and subassemblies: the largest module was IIRC about 22 tonnes, while the ISS itself is around 420 tonnes. The Soviets pioneered this with Mir, and ISS was designed around a core that was originally intended to be Mir 2.0. So we have quite a bit of experience assembling one big structure in orbit—a 25 year learning experience, basically, which has given us a toolbox of standards for docking adapters, compatible modules, external manipulators based on the Canadarm, and experience in on-orbit refueling and resupply. Starship is big and (in theory) cheap, yes, but it's not obvious that we can't do this stuff with smaller and pricier tools. Apollo didn't go for on-orbit assembly because they were in a blinding hurry (JFK set the "by the end of the decade" goal in 1961-ish) and it's taken us 25 years of plodding to get there. But we could do it now.