Why is Unity the most popular engine?

Unity was one of the first general purpose engines that was made free to to everyone.
Sure there was Torque Game Engine but that engine was so specific to an indoor online FPS if you wanted to do anything else, you had to do A LOT of work. Have fun ripping out server/client code for your single player offline game! It was horrible.
UE3 was almost as bad. If you just wanted a rendering engine that worked on a wide variety of hardware, Unity was a holy grail. For the years I used Unity, forum members replied quickly with excellent solutions.

As a VR developer, Unity has some far better official support from Oculus and Google.

Want to build a GearVR game with a debug signature so you can send the APK to anyone and they can run it?
That’s a Unity exclusive as I write this.

Want a nice Google Cardboard starter kit that easily lets you switch between stereo rendering(rendering images for each eye separately) and regular single screen rendering realtime so you can navigate menus via touch screen like a regular smartphone product but change over to VR when the goggles go on?
Another Unity exclusive right now.

Previous users mentioned some other VR related Unity exclusive features for other platforms.

There’s so much really good free stuff in the Unity marketplace.
Unreal community members are putting out some amazing free stuff too but you have to hunt for it.
If Epic wants to keep the marketplace a marketplace for selling, fine.
But this engine seriously could use a less-moderated hub for freebies too!

I tried Unity and if it wasn’t for the kind people in the community giving me advice or freebies from the marketplace, I never would have gotten anywhere.

I’m a designer and not a programmer so I really REALLY like Blueprints as Blueprints have let me create my own game logic at a level I haven’t been able to accomplish before but the feature gap in VR hurts.
I know the folks at Epic have a lot of ground to cover. I hope they can convince Google, Oculus and so forth to give all their Unreal plugins the same features as Unity but that’s possibly out of Epic’s control.