robert piepenbrink, you are correct: 3D printing would allow us to scale our figures to precisely 15mm/20mm/25mm/etc. I have thought about that, long and hard.
I spent the last 15 years trying to collect figures which matched Gary Gygax's size ratios he listed in his 1978 AD&D Monster Manual, so that I could truly see his monsters in their proper sizes relative to Humans, and to one another (Gary's Elves were 4-5 feet tall, not 6+ feet tall; Goblins were only around 3-4 feet tall; Gnomes are shorter than Dwarves, with larger noses…). I was partially successful: I bought figures that matched the correct millimeter sizes, based on a 6-foot tall Human being 25mm tall. It took a lot of research to find suitable figures.
In the end, though, it proved impossible as sculptors go their own way, with their own size interpretations -- no one followed Gary's sizes accurately, even with me mixing different scales to fill in the missing sizes of various races (1/72 scale figures helped fill in several missing links, however). The 3D printing option would have solved my dilemma, but 15 years ago, appropriate STL files did not yet exist for everything I was looking for. Back then, 3D printing was still too young, for my tastes and abilities.
Instead, I did the best that I could with what the market offered. It was a blast to do the work, find figures in the correct proportions, and to paint them as Gary described them. The man had a gift with color schemes and size ratios that most of his fans will never see. Heck, Gary gamed with mostly 40mm Human figures at his sand table! I assumed that since he referenced 25mm figures in his 1979 AD&D Dungeon Masters Guide, that he gamed with only 25's… Nope. But that really underscores his genius in proportions and color schemes, for me. It was/is a fun hobby unto itself.
My figure collection is too big, too well developed, to go the path of 3D printing now, after 30+ years of collecting/building my armies. Cheers!