When was the last time you broke up a single instance of sex into a dozen or so blocks over the course of a week? It doesn't matter that they don't need to be consecutive hours, it still takes hours, which means it can't be done nearly as frequently as something that takes seconds.
I think you're missing the point here. By any measure, whether a year—"fewer than half of all adults reported having read a book of any kind in 2022"—or a day—"the proportion of Americans who read for pleasure on any given day fell from 28 percent in 2004 to 16 percent in 2023"—there is time to read books.
The relative amount of time it takes to read a book compared to the time it takes to place a bet is largely irrelevant, because reading books is worth doing, and there is time for it. If you want, you can read and bet, on the same day!
It's not necessarily true, however, that gambling can be done more frequently than reading, because gambling requires money, and if you keep gambling a lot, you'll likely run out of money.