From what I have read (I don't do 3D modeling myself) Blender has overhauled its UI significantly over the past couple of years to great praise of a lot of people.
This is exactly the reason. Most 3D software has esoteric UIs, but Blender's workflow was extreme. Since its initial OSS release (2.4?) the UI has matured and changed significantly for the better. Its far more approachable now, and follows paradigms that every other solution does. It fits nicely in the pipeline alongside tools like Houdini.
Is there something that makes it a first choice for many professional users?