They felt that people were playing her in a way they didn’t like.
If you didn’t care about something you wouldn’t bother changing it.
Blizzard’s testing internally may also not be representative of the overall player base. You’ve got a bunch of people that have probably been playing with and against each other for 1,000 hours +.
Making Brig squishier royally messes her up in play with low levels of coordination as your team isn’t going to bail you out much or capitalize on the opportunities you provide.
The thing is, that probably is rarely the case in Blizzard’s internal testing considering the time they play together and the social pressure.
The old Brig at times was capable of covering for a lack of teamwork and that’s something people that like teamwork don’t love.
I think the Overwatch team released a product that didn’t do what they wanted it to do and was perhaps more successful because of that. They’ve gradually been making the game more into what they want it to be and for some people that’s great and for others it stinks.