Clearly you haven't worked with corporate design departments. The last mock I saw from one particular company had every single font size ranging from 10px to 20

Clearly you haven't worked with corporate design departments. The last mock I saw from one particular company had every single font size ranging from 10px to 20px until we worked through it. The spacing was even more lackluster. I think this mostly stems from similar issues as spaghetti code often does — unreasonable deadlines, multiple teams sprung into action in parallel with little to no coordination and so on. Usually people claim to know how these things "should" be done, but there's always a "but".