brainlet here, I just can't wrap my head around the concept of steam turbines getting bigger at later stages

I get the idea of having a rotor that gets pushed around, and a stator that redirects flow onto the rotor, and doing that over and over, but then each stage starts getting bigger and you start reading about how it's to accomodate for the expanded steam but like, it's a gas, it adapts to the turbine's volume not the other way around
and sometimes you'll see mentions of how i's because the steam has lost energy and has less pressure and making it expand compensates for that but, wouldn't increasing the volume just lower the pressure further and make things worse?