I think it a misconception to say classical music is less popular than it was before. I would say it is probably the opposite.
There has always been music created by and for the masses. Think of it, you are a part of "the masses" and there is no such thing as radio or CDs, or MP3s, etc. You want to listen to some song, you probably do not have the means to listen to classical music. A small orchestra requires a lot of people and if you are just getting your three dinners, a few rags to wear, and a mean place to live, are you going to spend the effort to hear a piece of classical music?
So, why is it not wildly popular these days? I would say classical music suffers from the fact classical music aficionados often tend to large ponderous slow pieces, pieces that are boring especially to those new to classical music.
A person's intro to classical music should be to fast, light, and lively pieces. One of my first classical CDs was a CD of Vivaldi concertos and I found them so much against the stereotype of classical music and so refreshing.
It is up to us who appreciate classical music to break down the stereotypes. When with a friend find a lively easily likable piece to play. Play something they are likely to be familiar with and do not necessarily play the whole work, just the movement they will be familiar with.
The attitude I talk about is captured by something I was reading recently. The Wiki on the 1812 Overture. On the show Niles reminds Fraser when young he [Fraser] thought the 1812 Overture a good piece of music, Fraser than goes onto wonder if he was ever THAT young. The 1812 is a good piece, it is popular and that is what many who listen to classical music resent and that attitude holds back more widespread acceptance of classical music.