on disc 2 of SKOM there's a spiel by one of Metallica's management (Cliff Bernstein?) which basically says it all- they've got millions in the bank, they've got their wives & kids to spend time with and beautiful homes to live in, car/art collections etc. - what motivates them anymore to go out and make angry thrash metal?
Dave Mustaine's still bitter about getting fired from Metallica, and Megadeth being no.2, so that motivates him, like a hare he can never catch, but Hetfield and Ulrich haven't got any incentive.
they've done it all.
I just watched on youtube Dave Navarro interviewing Mustaine recently (Navarro comes across as a lousy guitarist), where Mustaine says of Phil Towel- "they referred to him as "The Connector"- I saw him more as "the account drainer"