The context is that we're primarily a design company, the front-end is a way to express our designs.

A big reason for me is that I want the bigger group in our company to experiment with several CSS techniques to grow as front-end developers. If I (as a manager) set a constraint on one type of CSS it is difficult to learn more.

As an agency it makes sense to have broad capabilities. I think as a freelancer it's super fine to just constrain yourself to what you like, as you state there is huge demand out there.