OP asks a valid question, one that I asked myself when I started thinking about buying a tractor. I started out big, but ended up small (2320 w/ attachments).
I grew up on an Illinois grain farm that eventually grew to about 2,000 acres with machines to match, so I never thought of the CUTs as serious tractors.
Years later, I live on 40 acres of thick Michigan woods with less than 2 acres to mow. All that's tillable are some large-garden-sized plots. My first (and second) tractors were 1950 Farmall Ms. They are simple, well built, and the price was right. Anyone who knows that tractor knows it's a large-framed tractor, but to me even that was small.
Still, the M was too big for just about everything I wanted to do in the woods. I simply had trouble squeezing through the trees. It was way too heavy to even think about rigging a finish mower for the yard. The M took up a huge amount of room in my shed. The Ms power (37 hp with high torque?) came in handy a few times (using a loader-mounted blade to shape trails and yanking some small trees and stumps), but most of the time the tractor's size was just getting in my way.
That's when I understood the attraction of the CUTs.
My 2320 is far more useful to me than the larger M ever was (for lots of reasons, but also for its size). Yes, there have been a few times I've wished for a bigger tractor. But not near as many times as I used to wish for a smaller, lighter one.
My dad and brother who still farm make fun of my little tractor. If I ever buy the 20 acres next door which has a much larger tillable area, I might have to move to a bigger machine. But for now, the little one gets the job done when the bigger one didn't.
Joe