Earlier quoted context omitted.
For a resistance to develop, ebola that has been exposed to the treatment inside a hospital has to escape back into the wild. There are significant barriers in the way of that. If everyone on penicillin was kept in an isolation chamber, the effectiveness over time would be different.
As someone who works in a hospital, we can bleach every single patient room, wear all the PPE we want, but pathogens will always spread; the only question is when, not if. Even in an isolation chamber a resistance to penicillin would develop independently of each other as penicillin resistance is usually predicated on a mutation in the penicillin binding protein.
While partial resistance can be encouraged in a single person, that doesn't matter if it dies inside them. And if a resistance mutation happens in the wild, away from drugs, there's no reason to expect it to spread at all.