Part of the answer is sure to be that there are more people. In fact there are, I believe, more people alive now than have been alive in perhaps the entire past history of the human race. Since a certain percentage will be scientists/inventors/technologists, of course the inventions and improvements are coming thicker now than they were 500 years ago.

Others might give answers of how much more forward-thinking we are than our ancestors, and other such "chronological snobbery," but while part of the answer may be cultural -- look at how long technical progress took in Japan, or even more extreme, China, both of which had high civilizations but which did not encourage invention or originality until rather recently -- I believe that the key is the geometric increase in the Earth's human population.

I'm sorry this is such a sketchy answer; but there are not readily-available ways to measure such a thing. I'm sure you can think of something... like a search of patent-office records.