The primary tradeoff of initcwnd is setting a reasonable window before you've learned anything about the path. BBR has little say on this because it takes, in relative terms, quite a while to go through its phases. An early BBR session is therefore not really superior to other congestion controls because that is not the problem it is really focused on.
Jacking up the initcwnd, you start to risk tail loss, which is the worst kind of loss for a sliding window.. especially in the primordial connection. There are ways of trying to deal with all that but they are loss predictions.
If you are a big enough operator, maybe you have some a priori knowledge to jack this up for certain situations. But people are also reckless and do not understand the tradeoffs or overall fairness that the transport community tries to achieve.
As other comments have pointed out, QUIC stacks also replicate congestion control and other algorithms based on the TCP RFCs. These are usually much simpler and lacking features compared to the mainline Linux TCP stack. It's not a free lunch and doesn't obviate the problem space any transport protocol has to make tradeoffs on.