yeah i dont get why they feel the need to use unreleased tracks
even dettmann did it, its a thing now.
maybe they think, if they play released tracks, people will not like it.
Mix CD is not "popular" or "important" like it was in 90's or early 00's. There are plenty of mixes online available for free that are better than commercial ones. Podcasts, promo mixes, live recordings, etc.
Since commercial dj mix does have to be special in some way so it can be "standout" in the sea of mixes today and stick around for couple of years, it is easier, imho, to pack it up with unreleased tracks than select 15 tracks "which will be put together in special way that you will listen to it again in couple of years and say "wow, this was/is masterpiece ahead of its time".
With unreleased tracks it is "special, not ordinary, interesting", and hopefully
won't grow old soon. Also, you have nice platform to release your music.
I'm quite interested if any of commercial dj mix released in last couple of years will become "classic" and worth listening in lets say 5 years from today.