Because we live in an era of specialization. Look at a companies job page - even startups have silos. I don't think this is strange or unusual. Its hard to be good at everything. If I'm spending 8+ hours per day doing sales, where am I going to find the time to be good at other things? Most people are working for the weekend or to spend time with their families. Diving into far off subjects related to work isn't always exciting.