Let's say you earn a million dollars a year (most of us earn far less). At quite a few companies, a 50% decrease in your productivity (and changing browsers is nowhere near that) would cost the company significantly less than dealing with the fallout of any of the following:

* A user intentionally leaking sensitive documents outside the corporate network

* A user installing an infected browser extension that gives attackers access to corporate resources

* A user accessing malware or ransomware which infects corporate resources.

That's on top of the cost of having the IT department having to debug issues among users with bespoke tool sets which can often interact in unintuitive ways.

There are many stupid ways that companies "optimize" costs that cost them more in the end. Standardizing the browser and extension set for data loss protection is not one of them.