I've had this discussion before regarding the lack of great composers (like Bach, Beethoven, Mozart) in modern times. The answer is so obvious that many people overlook it.
The period that roughly runs from 1600 to 1850 was a unique time in human civilization. For the first time, people with artistic ability were able to completely devote themselves to their craft thanks to patronage - a practice where wealthy individuals (usually in the ruling class) would "sponsor" an artist by either taking him into their household as a servant or providing financial support.
Yet this period of time was also before television, radio, mass media, and the countless other distractions that occupy our modern lives. So these artists and composers were basically working on their craft from sunup to sundown with little or no interruption from outside sources.
It is hard to imagine today what everyday life was like back in the days of Johann Sebastian Bach or Ludwig Beethoven but if we could, we would likely find it incredibly boring. So if you were a composer during those times, well, that is pretty much what you did the entire day (when you weren't teaching students or conducting performances of your compositions).
In sort, there are simply too many distractions in our daily life to ever attain the compositional skill set of even a Handel, Haydn or Schubert. Imagine if Ludwig Beethoven was around today, fighting traffic jams on the interstate to get to and from work, checking his stocks on his home computer, watching the NFL playoffs on TV, flying to places like New York, Chicago and Los Angeles to meet with orchestras performing his works, downloading the latest John Grisham novel to his Kindle, playing Wii video games with his nephew, meeting with film directors who have contracted him to score their movies, trying to get his laptop to boot up so he can get a little composing in before the Jets-Colts game...and on and on.
While Beethoven would still be a very successful composer today based on his abilities, he'd likely never be able to produce works on the scale of the Fifth Symphony or Missa Solemnis as he did back when there were not all these distractions of modern life.
Because they did not have air travel, autos, electricity or the Internet in the 18th century allowed Beethoven's or Bach's genius to develop?
They had their own social networks back then which kept them busy...they had to do much more for themselves in order to have food and clothes. Many of the middle class learned to play instruments and anxiously awaited the latest sheet music of contemporary composers so that they could get together and play them.
Bach worked for the church essentially his whole life, loved his wife and his many children and still put out a cantata per week. Mozart's music came to him essentially "finished" in his head and he needed to find the time to transcribe it; Beethoven worked and re-worked pieces for DECADES.
Musical geniuses are born and the times they are born into mold the music they make; if Bach were born in 1785 rather than 1685 his compositions would have been very different; and perhaps he would not have even been remembered today.