Just because Unreal does it doesn’t mean it’s “popular”. I’m not familiar with any other game engine that has something like this as a first class feature.

The reason blueprints exist in UE is because they needed a way to allow non-expert programmers on the team to write code that isn’t C++, but they didn’t want to use a high level scripting language like Lua.

IIRC, Sweeney said (on Twitter) that in the past, it was a burden to constantly be designing and maintaining language bindings for scripts, especially with a rapidly changing engine.

Also, (I’m guessing here), blueprints result in less bugs since it provides static typing and makes it possible to do some advanced visual debugging. These are things that, even if they were available in a language like Lua, they would be intimidating and/or uncomfortable for the artists/non-programmers on a team. Plus I’d imagine that it’s relatively easy to produce some highly optimized code from blueprints, maybe even compile it to native instructions.

It’s also probably no coincidence that the visual node-based concept is used a lot in other tools used primarily by artists, like for material creation.