God I loved the ps1 driver games, they were the best of the series. Unfortunately the games you mentioned and many others will probably never see the light of day, probably until sometime after the PS4 is released. The folks at the PSN store have no desire to make these titles available for us. They will tell you that its the publishers responsibility to make them available, and the publishers will tell you that it's the PSN's incompetence that keeps them from being on the Vita.
I think that you are paraphrasing the publisher's response. Few of them would ever say that publicly. The truth is that the publishers can put any PS1 game they own the rights to in the Playstation Store, and make it available on the Vita. Sony isn't stopping them. But they have to package it as a PS1 Classic, and it has to pass certification testing on each platform, just like any other Playstation game that is released. Both of those cost a non-trivial amount of money, and for the vast majority of PS1 games publishers doubt that the game will sell enough copied in the Playstation Store as a result of being available for the Vita, to make back their investment, plus a profit. That is why they don't do it. Would more games be released as Vita-compatible PS1 Classics if certification testing was paid for by Sony? Sure. But someone would end up having to pay for that one way or another, and if it isn't the publishers, then it is going to be the customers. Sony has no commercial interest in selling another publisher's games.
Okay, then why is it that if you go to the UK PSN store there are titles that are available and playable on the Vita there but not here. For example, Driver is available in the UK and playable on the Vita, that goes for MGS Portable Ops as well. Unlike MGS, Driver isn't even available on the NA PSN store.
Now statisticlly speaking the North American market is greater and much more profitable than in the U.K. So your argument that publishers or Sony feel that it is not profitable to make these games available is severely flawed.