I agree with you. How many founders are able to find success twice? How many thrice? It's shockingly low, even amongst the most respected tech magnates.
Here's an example I like to use which I'm sure will be controversial, and I want to preface this by saying I've personally met and respect Justin Kan. But if you look at his history of starting companies, he only gets worse with time.
https://en.wikipedia.org/wiki/Justin_Kan
He started with twitch which sold for just under $1 billion, then had SocialCam which sold for $60 MM, he then sold Exec for an undisclosed amount, and after that his initiatives shut down or are ongoing. Obviously he still has time for some big exits, but the trend doesn't make it look like he's learning.