Dev tools are part of all browsers. Even Safari, which tries to keep things very simple, ships dev tools on the stable version. I really don't see the point in removing them.
They are very good to have available to everyone.
The thinking is that users are a danger to themselves and will be tricked by threat actors to add some CA cert to the trust store, paste commands into the js console, or download and sideload malicious extensions no matter what controls are in place so therefore these possibilities must be removed.
To this day, firefox is still the only browser that prevents its users from running custom extensions without Mozilla's blessing, likely motivated by the same garbage argument.
I have very little hope for Mozilla at this point and sincerely hope that they fail soon so that better open source browsers can take its place.