Yeah they do cop a lot of crap, and to be fair some of it is justified, but I think a lot of it is carried over from the 80's and 90's when they looked goofy and played differently to the other bands in the Big 4. Look how many people still to this day claim Anthrax shouldn't have been in the Big 4, despite also knowing that the big 4 was about money and sales only. People wanted to dislike the band years ago and that dislike has carried through to today to where some people are too embarrassed to even admit they like the old stuff in case people think they are less 'metal'.
However because of their own doing the last decade or so has not won them too many new fans. Even on FB where they do post regularly (today it's the 35th Anniversary of ATL), they don't often get the number of responses bands like Testament do, and no where near the responses Slayer do. Obviously FB responses are not the only thing to measure popularity by but add to that lower record sales and smaller tours and it's not hard to see they are a shadow of what they used to be. I don't think they'll ever get back to where they were but they could do themselves a favour and start treating the fans they do have with respect and not just a cash machine they can remove money from when it suits them.