That is exactly the reason. Also, some libraries we are using are not on homebrew (and we cannot easily pin a specific version).
Another reason that we'd like to reduce the maintenance burden by using a similar setup for windows and macOS deps. Our dev team is small, and almost all of us use Linux. For macOS in particular we don't have anyone on the core team that uses it as their daily driver, which may also play a role when talking about the DX in macOS.
Mixxx dev and main author of rekordcrate here. The issue is that the format is an ancient proprietary format that does not have been reverse-engineered to a degree that we can properly write Rekordbox DBs yet (Rekordcrate is based on the work done here: https://djl-analysis.deepsymmetry.org/rekordbox-export-analy...)
Mixxx is entirely community driven: There is no company behind it, everything is done by unpaid volunteers.