There is no more inertia in the academic sector than in the software developer sector.

That is not true. In academia you have extremely niche research specializations and tenure as two major contributors to inertia. In general software development you have an enormous amount of career mobility.

Software developers learn new languages, new frameworks, new tools, new development methodologies all the time. A string theorist who decides to pivot away from string theory essentially has to start their career over from scratch. It’s not even close!