Do you know that as fact, or speculation? Because they still manufacture and sell hardware that is dependant on it, so it needs to be developed. And a recent update would suggest otherwise.
I could swear I saw Garmin's statement about it, but I cannot find it anymore, except one of the forum's moderator's statement, that basecamp is no longer actively developed (which is not exactly the same as abandoned, I admit. Sorry for bad wording). Perhaps my memory is playing tricks on me.
Anyway, last update was about 2 years ago. The 4.7.0 version that came in May this year was only to comply with new EU regulations concerning user data privacy.
All I can add is that I used to have regular contact with the BaseCamp developers but they all went a few years back. I've seen no evidence of any development in functionality. 4.7 was simply to comply with new regulations and Garmin have said they are releasing a 64 bit version for the Mac https://support.garmin.com/en-US/?faq=h2GdyqqKN11m0JielTs4V9&productID=52801&searchQuery=mac%2064
