Their early tone came from the alcohol/drug/anger/promiscuous sex induced era of their youth...ferocious, raw...thrash. There later tones reflect age, reduced alcohol/drug use, growth, experience, and desire to make more money by appeasing the mainstream. Neither wrong or bad...I prefer my rock n roll with sex, drugs, and anger...I prefer the earlier Metallica.
Bingo… these guys are not pissed anymore or have the drive when they were young. What do they have to be mad about? That’s going to be reflected in their writing for sure.