Is it just because it’s so much power that there’s weird components in there?
At face value, plugs are in general pretty solid! Like how many times in your life has a plug in your house just stopped working.
But to your actual point: I have a feeling they’re just badly engineered. Tesla ones are so much more reliable than third parties. I’m not sure if that’s because they break less or are fixed faster, and I suspect it’s some of both, but the difference is very large.
But a key issue seems to be that EA went crazy and made their chargers out of lots of different components in a panic to get started, analogous to the PC world where there are huge numbers of different parts configurations, and even if you have only 6 major charger models, your fix it tech probably doesn't have parts of all 6. It seems obvious this was a bad strategy, but they wanted to get their chargers working as fast as possible. Instead they created a permanent bad quality reputation that may never be fixed for EA.
But it's not just EA, other companies seemed to have no plan for fixing their chargers when they break.