It's entirely up to them how they decide to spend these first few weeks. They may be concerned about the baby's health as they are at more risk from bacteria and viruses when very young. It can be very serious, for example, if an adult with a cold sore kisses a baby and passes on herpes - this happened to a friend's baby and it was touch and go for a while. Perhaps they know someone whose baby became ill through something like this.
Even if that's not the case, the amount of contact with others is their decision .
It's understandable that you might feel hurt by this approach - especially if it wasn't what you expected.
I'm sure you love them all and will not want to say anything to jeopardise your future relationship with them.
Send a card and gift and wish them all the best.
You could say you're looking forward to seeing them all whenever they're ready and you'd love to have them round for dinner, babysit, pop over and help with household chores.. or whatever you feel is appropriate to offer.
I'm sure in a few months, this will all be forgotten and you'll be a big part of your granddaughter's life. All the best.