why they wouldn't rather have a sequel to MGS4
Because what sequel could you possibly have to MGS4?
That game was explicitly made to completely close the whole metal gear saga.
The heroes are all retired and living away from military lifes.
The villains are all dead, their secrets are all exposed and their plots all thwarted.
And just as importantly (given the series focus on narrative), the game's have literally touched on almost every modern war related theme (even if poorly most of the times) - genetics, memetics, the impact of the zeitgeist, 5th generation warfare, conscription vs pmc outsourcing, the war economy, nuclear proliferation, physchological trauma, the ideological roots and fruits of the cold war, transhumanism, mass surveillance, loyalty, loss and love
There is nothing new for the series to explore and the fans don't care about that part of the timeline (this is part of the reason why MGRising's plot worked in way)
I doubt Konami will remake MG and MG2
I this remake is successful (which is highly likely), I have no doubts Konami will remake the Metal Gear games
It's just too tempting
If it needs be they will perform life extending cirurgy or rituals on Richard Doyle to make sure he reprises Venom and Big Boss for those two games (or just MG2 and for MG1 they use Keifer)