This one shows that Israel provides Gaza with no less than ten separate electricity feeds, three of which are split off in Gaza itself. Israel provides far more electricity to Gaza than the Gaza power plant does,
My guess is that Egyptian fuel is cheaper, and perhaps Hamas can more easily tax and redirect the Egyptian fuel for their own purposes.
However, in May and June, Israeli exports of cooking gas went much higher while Egyptian exports plummeted. Apparently, the cost of Egyptian cooking gas soared (some blame Hamas, Hamas blames new regulations) and it seems Israeli gas became more affordable by contrast. Gazans were very angry at Hamas when someone published the raw costs of cooking gas from Egypt and the Gaza costs were double that amount.
As usual, what we see in the media is only a tiny portion of what open sources can tell us, and the open sources are only a tiny portion of what is really going on. So-called experts are working with very limited information yet they confidently tell everyone else their analyses as if it is based on all the information - and it never is.