So why doesn't anyone make nice large bras?
I would imagine because structural concerns become more important with larger sizes, that is, it becomes more important that the garment actually hold and support and not injure you (this being a rhetorical you, as I have no idea whether you are female or large-chested) than that it look nice.
With smaller sizes, where the support job is much less structurally demanding and comfort is much easier to provide, more concern can be given to aesthetics.
and correct me if I'm wrong here - there is a rebuttable presumption that guys like bigger breasts.
You're not wrong, but you're not entirely right.
guys like bigger breasts.
However, most guys simply have some range of attractive, where smaller or
bigger are theoretically sub-optimum.
Most guys have some standard of "proportional" as well. Many would also prioritize shapeliness above size.
Some have a "bigger is always better" and some have a "smaller is always better" standard, but I imagine both are in the minority.
And many just take things case-by-case.
Generalizing is hard.