Saturated genre (trance) vs. unsaturated genre (orchestral/ambient - always has an audience). Also, @Magdelayna remixed Hans Zimmer, who has a much bigger worldwide name recognition than The Thrillseekers and Solarstone.
That being said, Magdelayna is probably getting a lot of views and subscribers from people who like Ambient and Hans Zimmer. The Thrillseekers and Solarstone get subscribers from their fans. That is evidenced by the difference in Facebook likes that Magdelayna talked about in the comment above.
Thats true,if theyre gigging around the world they will get a lot of social media followers - that explains that.
Another strange thing ive noticed,if you take their two biggest tracks - Synaesthesia & Seven Cities - the top played videos of them are uploaded by random people...you normally see a bands biggest tracks uploaded by their own channel,and then be the top hit on Youtube for that track.
I keep thinking some of the biggest Trance producers have missed a trick with their Youtube channels - id also point to MIKE,Airwave and Lange who also have relatively very low subscriber numbers.