I'd say there's probably more roles out there to move up into. Companies may be using Microsoft 365, but could be using other providers for their cloud infrastructure. They might also expect their cloud engineers to know multiple platforms. I had experience creating highly available environments on-premise before breaking into Azure.
This is a good point. The number of M365 jobs out there probably outnumbers Azure jobs. And the M365 jobs typically need just one skill, whereas a typical Azure job will require many. And one is a logical step from helpdesk, and one is a total focus change.