Adobe used to have this feature in their typeface format and type design tools in the 1990s. The format was called “Multiple Master”, see
https://en.wikipedia.org/wiki/Multiple_master_fonts and
http://blog.typekit.com/2014/07/30/the-adobe-originals-silve.... (Metafont also has this feature.)
In practice, type designers found that making such fonts took dramatically more work, and typographers/publishers weren’t willing to pay commensurately more money. So it didn’t see much adoption outside Adobe.
As a result, the format died out, and we stuck with descendants of the original PostScript font format.
More recently, many companies (but especially Adobe) ship “pro” typefaces with separate fonts for various “optical sizes”. Again, producing these takes a lot of extra work, so most type designers don’t bother with it, and because it is designed to work with standard tools (which don’t have special knowledge of the feature), typographers/designers must explicitly choose which optical size they want to use in each context. So in theory it’s inferior to the Multiple Master format, but in practice it is backwards compatible, which ends up being more important.
Apple can solve this problem for their UI fonts specifically, because they have full control. Unfortunately, they haven’t offered these features for use with other typefaces.