Lots of legacy apps use bit-mapped graphics instead of vectors. Xaw and Motif are both not resolution-independent toolkits but getting them to support integer scaling (with line-doubling) would be far easier than trying to implement fractional scaling plus anti-aliasing.

Apple literally doubled the resolutions of their pre-HiDPI screens for their current screens and then scaled their interface by 2x for the default OS builds, so if their interface is too big for you then it probably has been since Mac OS X came out.