I have a similar setup (older Ubiquiti AP-AC Pros), and for me it was just a dislike for Ubiquiti's cloud-connected/distributed management architecture. I don't want my network hardware phoning home or depending on the cloud or even other components on the local network for any functionality. (It's sorta similar to how I feel about Apple; I really like their hardware, but am not a big fan of their software.)

I also just in general trust an open source project (sure, I know, I haven't personally audited the source or the build process) over close-source manufacturer firmware.