I can't show you a certain source, however I'm sure you can find relevant discussions on Steam. Apparently he used other peoples textures and models for some of his assets without permission. When the original authors brought this up, he went rage and removed everything. Now he is back, it's been a month or so. He is back by the name "Flame" and released some new assets, however they are marked as incompatible. He redirects you to some other website and asks for money to have his assets, both new and old.

ApollonDriver, thank you for the update. Do you have a source for this info that I can reference?

he removed his workshop because he got copyrighted

Is there a non DLC version of this yet?

There's still more than a few planes left in the Aerospace collection, despite the loss of so many cool ones. https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1877875254

Unfortunately, the all vehicle and props provided by CRISGAMES have been removed from Steam. There's not explanation as to why. I'm leaving up the park buildings for now in case they are restored and also to as a location for others to learn about the missing props in case they used them too.

Perhaps you know where to get this prop?