The other thing to keep in mind is that Di'Anno left (was fired from) Maiden because, in his own words, he "was snorting . . . coke . . . non-stop, 24 hours a day, every day."
Same with Ozzy and Sabbath, and Dio left because of personality conflicts with Iommi and Butler (same as Tate and the rapidly destructing Queensryche). Kiske left Helloween because the band was imploding from deteriorating personal relationships.
None of that stuff exists in DT. No one's drinking heavily or doing drugs and, by all accounts, they all like each other a LOT. Same with Rush. Rush may not have been "cool" in the '90s, but that was no different than the '80s or the '70s, but by the '90s, they were all financially well off and as successful as they wanted to be. One of the reasons why Rush remained popular with its fan base for four decades and had a massive surge in popularity over the last decade of the band's existence was because they didn't change members. The members' loyalty to each other engendered the same among fans.