The numbers are tied to real rates
The first upgrade costs 15 clicks, which a 400 CPM hand banks in a little over two seconds. The whole price curve is set from measured click rates rather than picked arbitrarily, so progress reflects what your hand can actually do.
Per-second income is deliberately weak early and dominant late, which is the shape every incremental uses: it turns an active clicking game into an idle one, and the crossover is the moment the genre is built around.