With so many options for 3D modeling software, why would Blender, a software designed to make 3D animations, be the most popular choice?
First things first: you don't have to pay for Blender. It is offered free of charge. If it works for you, you always have the option to donate, but Blender doesn't do anything to force this point. It is free now and forever.
While it's true that Blender is designed for animation because it covers everything from a blank canvas to a finished animation, it contains the ability to model objects, and it's one of the most robust suites of modeling tools anywhere. Learning Blender means that you may never need to learn another 3D modelling software.
Blender is in constant development. If it doesn't have a feature you need, chances are that it may one day. Blender's developers are constantly responding to their audience.