Right, and that station is in LEO and getting resupplied pretty frequently.
We do not have any examples of space orne and isolated systems supporting human life for months, especially beyond the magnetosphere.
The ISS's orbit is not particularly stable and it needs regular reboosts which leaves everything else scheduled with this in mind.
Providing food and other necessary resources for a long stay would not be especially difficult, but there's no need for it, and that leaves more volume to store other stuff.
The ISS, despite being a 'station', is very small with a pressurized volume of about 900m^3, about 100m^3 less than Starship. The linked capsule design also means the real usable volume is substantially less.