You follow tennis, so you know all these players. For a sport to continue to thrive it needs people at the top of the sport that people who don't follow the Strasbourg Open can recognise. Tennis is quite fortunate I suppose because most of their big events are held simultaneously with the men's, so they are guaranteed funding and sponsorship even when it doesn't have people like Serena Williams to carry it but people aren't tuning in numbers to watch the final on Saturday, like they will be on Sunday when Nadal or Djokovic are playing.
You do make some good points, and from a purely mainstream audience/sponsors point of view, it does help to have some high profile players.
From a sporting point, it's also nice to have a bit of unpredictability and a level playing field.
Osaka is the best of the "younger" players, she's already a big star, has 4 GS titles, ranked 2 in the world, and is still only 23.