Wrong?
Maier used Brownie, before TLRs and switched to SLRs, RF later on. She stopped using TLRs in seventies and was still taking pictures in eighties and nineties. She also used movie cameras for interviews.
HCB started not with Leica. And it wasn't just for few months before he started to use Leica.
Herzog tried Leica for Vancouver BC photography, but didn't liked it and he switched MF SLR and SLRs.
Winogrand used LEica RF for street, but for sports he might use Nikons SLRs.
Meyerowiz switched to LF for some time, because RF wasn't good enough for particular projects.
They switched as soon as certain camera type and format wasn't good enough. But Ansel Adams had many cameras to play with and it wasn't just in large league
It is not so quick and simple as you think. And "most" doesn't mean all.