This was a particular class of vaguely upper-class ladies (ones who could afford harpsichords) who learned to play simple pieces. (In the case of Maria Barbara, of course, not vaguely, and not simple pieces, either). I think the men of that class spent their time in philosophizing.
Presumably, although CPE’s dames were rich enough to afford harpsichords - the next generation after Couperin’s pupils. The 19thC girls merely had to be ‘respectable’ (in the economic sense, not in the moral sense).