Haha, I’m here, better late than never I guess.
Areivim, by asking “where’s the mitzvah to do this” you seem to be implying either that women shouldn’t do it, or that it’s somehow strange or unnatural for them to do so. Guess what- there are many mitzvot that women are not commanded to do that we nevertheless do because we can. How many women do you know who bentch lulav and etrog on Sukkos? Well, we don’t have to do that either, but I can’t think of any frum women I know who don’t do it. As long as it doesn’t interfere with other obligations, why not? In fact, isn’t it commendable to always be looking for more ways to serve Hashem? As someone pointed out, there are considerations of young children, but for unmarried women, women with older children, childless women, and women who have secured babysitters, staying up all night learning on Shavuos can be a wonderful opportunity.