Why provide for anyone else (except in dire circumstances) when you could provide at a more comfortable level for your own household? The grandparents in this case worked for it!
Babysitting is fine if someone wants to do it but it's not an obligation. In this case, the grandparents said "no." It's not lack of love, it's freedom of choice and the right to self-determination.
IMO, the grandparents here don't seem mean or stingy, they're simply keeping the responsibility where it belongs.