And how exactly did the BSD license make creating Valkey easier? GPL and BSD licenses both have the source in the open. Anyone creating a fork, can easily do so for either BSD or GPL licensed projects. Since Redis is a database, which the user won't be using a binary of, even using a fork of a supposedly GPL-licensed Redis would not require you to share your modifications with your user, same as BSD.
The BSD license made forking Valkey easier because it ensures that everyone has equal footing. The GPL, especially with contributor license agreements and the like, makes it much more easy for a single party to control the direction of the product. For another example of this happening, look at MongoDB. It started out under the AGPL, but was rugpulled to a non-free license.