it has to do with preferences, era and trends.
contemporary (bikes now) bicycles tend to have 74~75.7 deg. head tube angle, while eary mid-school bike range from 73 deg. to 74, late mid-school from 75 to 76.5 deg. head tube angles. the lower the number, the slacker (slower) it is, some feel slacker H.T angles are more stable when doing tricks (rolling/ scuffing), but requires more 'work' to get into positions.
the same can be said of C.S lengths - longer= slower, harder to pull into position (a manuel for example) but easier to 'lock-on';
shorter= quicker, easier to get into position but it's harder to maintain said position (especial on rough, uneven ground).
that said, if you look at competative pro-level riding today, most take place in tight squares with flattish surface; riding wise it's quick links, body varials and fast, tight spins.
so a bike with steeper 74.5~75.5 H.T angle, short rear end make sense.
i rode bikes with T.T of 20.5" to 18.2 (tried out a friend's 17.9 garuda too), and i'm 5'2.
20.5" for street is comfy, but i'd think 19.75 to 19" for a hybrid would be better;
19.5 to 19" for flat is too long - can't do deathtrucks type of tricks (asians body-type tend to be torso long, legs short)
18.75 to 18" would be great for flat, depending on personal set-up and headtube angle prefrences.
17.9" and shorter would be doable but needs careful setting up of parts, probly great as a training bike.