Note: if you have not heard of the Interplanetary Transport System or ITS, it was a 2016 concept for a fully reusable rocket which could deliver 300 tonnes of paylaod into low earth orbit. It didn't die, but it was downscaled instead in 2017. The only differences between it and the current evolution (the ITS was one of many different rocket concepts by Elon Musk that evolved over the years, but it was the largest of them) is that the ITS was to be it being made of carbon fibre composite and its larger size. It is now Starship, with 150 tonnes of payload to low earth orbit.
Why was the ITS downscaled? It would have a lower cost per kg than Starship and would be suitablw for interplanetary missions once its tanks had been filled completely just once in low earth orbit. I'll cover some reasons that have been given and might be given:
- Doesnt fit in SpaceX's existing facilities. (Too wide)
SpaceX built a whole new seperate spaceport specifically to accommodate the size of the rocket, and work had started in 2014. As for their other facilities, they could upgrade those later when the project is not such a financial strain and SpaceX is making more money.
- Too bold/expensive
No. The current Starship is 9m wide, uses the same Raptor engines, and is also fully reusable. So it wouldn't be that much bigger an undertaking than they are doing already. The ITS was only different in that it was 12 metres wide (the current design and the ITS are the same height) and to be made of carbon composite (but SoaceX should stick with the stainless steel they were using for Starship if they return to an ITS sized rocket).