At least part of the problem is that they tried - there was a moratorium on Eskom developing new power stations etc for nearly 10 years because the ANC tried VERY hard to get outside investors to come in and set up competitive telecommunications and power suppliers etc. but there were no takers. (Don't ask me to prove this, because it is damn near impossible to find old articles and so on these days on Google.) I'm open to correction but I think it was only around the time of the problems with Koeberg that they caught a wake up and realised how deep in the dooh dooh they were. Anyway this is partly why we now have such aging infrastructure with no development to replace it.
Actually they didn't try very hard.
They invited investors to come in under rather restrictive terms and conditions that were never going to work.
Guess what, money looked at it and went you're crazy. You want us to invest, but give ownership away?
No-one bit, unsurprisingly.
The idea was solid, but the implementation was the usual ANC cockup.
Eskom worked well till about 2002 when it was taken public, after that point it became a mess of BEE and corruption. You can blame Thulani Gcabashe, Jacob Maroga for most of that, then the ANC "Chancellor House / Hitachi" scandal which we're still paying for.
It went substantially downhill from there...