Because most JL products tend to be more expensive than 'Brand X Audio' internet companies which have a HUGE following on sites like this where most (certainly not all) members don't really know a whole lot about car audio. They come on here seeking advice...'What do you think of JL-whatever' and immediately they're hit with 'Oh that's crap, it's way overpriced and you can get the same thing from Brand X for half that!' Most forum members won't know any better and will often believe this because the 'experts' (who may actually know less than them) told them so.
JL has many outstanding products and their customer service is top-notch. I think the retail price puts-off a lot of potential buyers...and the folks that hate on JL usually do so because they have settled for Brand-X because they couldn't afford JL and now they need to justify that decision by shitting all over the JL brand name. It's kinda sad really.
The reality is Brand-X is not the same thing and will not perform the same way. Not to say that the Brand-X's of the world don't have some exceptional products within their line-up's. But JL really puts a lot of emphasis on R&D and each products is refined individually. Hence the additional product cost.
All that being said there are a lot of other products out there that are quite good but little known or from little known companies. But this shouldn't diminish JL's general bad-assery when it comes to producing great products.
Just my opinion...I'm sure some folks may not agree.