1) We've seen that EVERYONE wants to be hokage. 2) How does it reflect on him as a kage if there aren't anybody better than him for the role? If he's the best available, then he's a good kage. Don't hate on a Hokage, just because you couldn't be one
Minato did way more for the village in one night than hiruzen did in his whole career as hokage...
Minato was the perfect choice to replace Hiruzen. No one was any better then that so he stayed as kage. If he had more trust in Orochimaru, he would have taken it.