Ask HN: Why don't big companies use bootstrap/foundation?
I've looked at many good products and websites but i don't see a trace of a css framework, everything is build in-house.
Bootstrap is a cookie-cutter framework, it is significantly more bloated than in-house frameworks that are tailored to only have code for the things you need (assuming you have competent devs). The same applies for performance, modularity, and extensibility.
On the other end, when a company grows towards maturity, it makes sense to have a design team for all their products that can experiment and design specific elements that are consistent not only between themselves but also with their branding, mission and strategy.