It’s a design decision Carolyn. Not many countries have (had) 4m. 60m is included as there are local allocations and a WRC15 band.
0.35% of activations have had 4 or more QSOs on 4m, that’s 772 out of 218656.
0.9% of activations have had 3 or less QSOs on 4m.
That’s more than 23cms for example. But 23cms is worldwide (or more worldwide) than 4m.
There was a period of regular 4m FM operation using the rather good Wouxun handheld which I don’t think is sold anymore. Likewise there was regular 23cms FM operation by people using mainly Alinco DJ-G7s. 4m has recently regained favour.
EDIT: sorry I thought you meant not including 4m not that 23cms didn’t work!