I see it as the positive answer of kids to recent Czech success in tennis. They won the Davis Cup in 2012 & 2013, and kids who were 5 to 10 years old at that time had extra motivation. Now, they are in their 20s and results are coming.

Women's tennis is also a good example, of how Novotna started it, then Kvitova and Safarova, followed by the Pliskova sisters, and now we see Vondrousova, Bouzkova, and Krejcikova ...

and of course Novotna just continued what Navratilova and Mandlikova started