Why? They have a fixed budget after all.
It also doesn't really make strategic sense to focus on the lowest common denominator. Chrome already has that group. The one place they could eke out a loyal userbase is specifically the users that Chrome fails to capture because they have unusual needs or requirements.
You have to be just mindbogglingly oblivious to not see how this has been one of their biggest problems the last 20 years.
Meanwhile, Brave's vertical tabs were done by a single developer.
Would you rather attrite a fraction of 95% of your users or a fraction of 5% of your users.
Without data you can invest your time into the wrong features.