1. Because it's most popular. Guaranteed support and "monkey see monkey do".

2. The adblocking is preconfigured, and non technical users trying to find the right extensions has a very bad history of unintentional malware. Ad block? Adblock plus? Ublock? Ublock origin? This is a great example of what floors a lot of technical folk who would be "why not just install ublock origin" and fail to understand the "why should I when I can just get Brave one and it works"

3. Most people don't use macs

Librewolf meets 2 and 3 (it comes with ublock origin preinstalled), but admittedly fails 1 quite badly.