[gfv]

>why do we measure time in hours, days, weeks, months, and years rather than in decaseconds, hectoseconds, kiloseconds, megaseconds, etc.?

We don't use them generally because at the time of French Revolution, due to taxes, standardizing the state units of measurement of physical goods was a much more pressing concern than time. (If I were to guess, there were no work hours limits, and thus it just hadn't crossed the popular mind). Weeks were changed to have ten days though.

That's not to say that they hadn't tried: decimal time was mandatory for a few years before they realized that there were too many clocks around, and pushing decimal time can actually turn people hostile against the then-new metric system.

We still kinda sorta use them in form of fractions of Julian days.