The version I read for Germany was that when the mobile broadband spectrum was originally auctioned off, the purchase price for the spectrum was too high. So the pensioners and other investors who bought in demanded a juicy return on investment despite overpaying, resulting in high prices and presumably less money for investments in the network.
For the fixed line broadband network in Germany, its quite substandard despite the country being generally good at infrastructure. The reason can be traced back to corruption, where a decision was made to rollout copper backbone instead of fiber optic, which was the original decision. Article in German but copy and paste with Google translate:
https://www.wiwo.de/politik/deutschland/langsames-internet-i...