I'm guessing that maybe he has a strong fondness for the role that made him a household voice. It did take a lot of convincing to get him back as Megatron the last couple projects. I wouldn't be surprised if Peter Cullen didn't twist his arm.
Point is, some voice actors are that well off that they can price themselves incredibly high, some have to dub Turkish Christian soap operas for a living and are grateful for the opportunity.
As for Pamela, I wouldn't be surprised if she wanted to almost completely walk away from voice acting to focus on a comedic acting career. Only cartoon I've seen her be a part of lately is Bob's Burgers, a show that employs a lot of guest comedians in guest character roles (including Key and Peele, but on separate occasions).
Point is, some voice actors are that well off that they can price themselves incredibly high, some have to dub Turkish Christian soap operas for a living and are grateful for the opportunity.
As for Pamela, I wouldn't be surprised if she wanted to almost completely walk away from voice acting to focus on a comedic acting career. Only cartoon I've seen her be a part of lately is Bob's Burgers, a show that employs a lot of guest comedians in guest character roles (including Key and Peele, but on separate occasions).