Yes, demo versions are available for most licensed plugins. Also, let's not change the subject. We all agree that Mulab is an excellent DAW with its own addons. If it wants to stay in this niche, it's OK, but then do not ask people what stops them from making it their primary DAW.
For me, the fact that it's difficult to run the plugins that I like is a very serious reason. There's no point in arguing about methodology of testing. It's a fact.
If developers want to get out of this niche, they will have to get demo copies of popular plugins and try to figure out how to make them work. As far as I am concerned I can use Mulab without CPU hogging plugins, but it's not going to be my main DAW.
I mean it in a most constructive way and apologize in advance if it rubs anybody in the wrong way.