I've been reading this for awhile trying to think of the right thing to say.
And I think I have it.
The thing about music today is, there is a lot more of it. Back in the 80s it was a lot harder to get your music out there, nowadays, anyone with some mates, a room and a few hundred dollars for protools and a mic can make an entire album of semi decent quality. This means you are going to have to get past a lot more crap before you are getting to the good stuff. You can't say "Metal is crap nowadays" just like you can't say "Jazz is crap nowadays" there is just more of it.
Also because Metal was fairly new in the 80s (10 or so years, half of that as a popular genre) there wasn't a lot to do. Now that Metal has established itself people are trying to find new things, new ways of approaching it. When people grow up with, or are fans of, the old ways, they don't want to see a bunch of kids come along and change the way something they love so much sounds/feels!