Tl;dr: Were bicycle frames in the mid-20th century generally longer than today?
This post asked about the length of a Soviet bike from the 1980s. The frame is longer than that of a contemporary bike the author compared it with.
I wondered whether that's less a question about Soviet bikes than about old bikes. Product design in the "socialist" countries didn't change very often; that frame design may have been decades old in 1987.
My very limited experience seems to support that idea: Most old bicycles I remember (often from decades before 1987) seem long and "comfortable". Among them are what we call "Holland" bikes (sometimes indeed manufactured in the Netherlands) and what I'd call "grandmother bikes", black long steel frames for an upright riding position. Of course there were contemporary racing bikes back then with different frame geometries; one possibility is that at all times short, agile frames for "sporty" bikes existed in parallel to long, stable frames for "comfortable" bikes. But I think it would be difficult to find such a long frame at all in the mainstream market today, so I think there is more to it than just a gradual shift in customer preferences.