-design is inheriently unique. You want your brand and your site to standout from the rest. A one size fits all design methology actually goes against design. A design framework for the web is like saying all stores should look the same. Even restaurants dont look the same and they are in the same usecase. Design matters and cannont be churned out like a factory product (or good design at least). There are 2 80/20 rules here. You can get 80% of your good design by adhering to 20% of the standards, yet its the last 20% of good design that makes your site stand out and the first 80% is just basic usability.
-dashboards are purely functional and not user facing (at least the admin dashboards I hope this framework is talking about). This is a great place to use a standard framework and get all the reuse out of it so you can focus on making your user facing site unique