Why so many sleep assistance apps? what kind of data are they collecting and how is it useful?

I'm noticing an increase in the number of sleeping assistance apps on the market recently. we obviously have sleep for Android which has been around for ages but now I keep getting all kinds of ads and even seeing it as sponsored ads on YouTube videos. the most recent one being for Pokémon Sleep .
how valuable is a data there collecting while we sleep and what kind of data could they be collecting?

ads ages android apps assistance collecting data market privacy sleep sleeping sponsored