^Well, Jinbei's status hasn't been revoked, yet. It's definitely teetering on the edge of being revoked, but for the moment it's still intact......
Anyway, it was ultimately the government's decision to form the Shichibukai. We already know that the marines distrusted them from the beginning (Sengoku's reaction to Doflamingo messing around with the marines in that meeting comes to mind). I suppose the government figured that the best way to battle piracy was to
think like a pirate, and what better way to do that than using some of those very pirates at their disposal? It's really not a bad idea in theory since the Shichibukai, as pirates themselves, have better knowledge of what dirty deeds are going on across the seas than the marines do. They also have the advantage of being less conspicuous amongst other criminals than a marine officer would. But most importantly, having powerful pirates on the side of the government would maintain the world's balance, as was pointed out so many times throughout the series. Remember how Crocodile was regarded as a hero in Alabasta? Seeing once-notorious criminals fighting for the side of justice would bring a ray of hope to the innocent folks who're suffering from piracy......
Yes, so far we've seen most of the Shichibukai betray the government in some way, but the way I see it, the government's still determined to keep them in power for the reasons I already elaborated on above. And if any of them DO end up getting their status pulled, they'll just get replaced. There's plenty of pirates for the government to choose from (personally, I still think the supernovas would make the best candidates
).....