Why did so many early / cheap calculators use 9V batteries?

[KF6GPE]

I had always assumed --- and maybe someone with an EE can tell me I'm wrong --- that the 9V was easily downconverted to 5V for TTL, and during that period TTL was cheaper than CMOS, which was newer. Getting to 5V with AA's or other batteries would require four, which is more bulk.

But that's just speculation on my part.