I agree. I taught myself CSS1 by reading the spec (it was limited, small and simple). CSS2 was a lot bigger and way more complex but Eric Meyer's Salmon book helped a lot.

One problem (20yrs ago at least) was that for a long time the specs weren't supported very well by common browsers. So everyone just prodded at hacks using trial and error instead of learning it. That approach never really went away even after support improved.