The answer is, of course, that there was just as much shallow and awful music then as now. The difference is that what people think of as "classical" is the best of the past few hundred years. Those who compare hundreds of years of "classical" (which wasn't a single genre in any case) to fiftyish years of rock are comparing the best of one to the mediocre of the other. And these days, record labels are (tending to "were") a patronage system.