I suspect several major factors have caused this decline.
First, the standard of living seems to have improved significantly in the Czech Republic since it joined the EU in 2004. Check out WH content before then (and even a good few years after) and then compare it to today's stuff: all the 20th century Soviet decor from before has transformed into Westernised Ikea-style modern design, and the cheap threadbare briefs the models used to wear now have Calvin Klein and Armani waistbands. It's fucked up, but a thriving economy/job market is probably bad news for porn.
I'd also argue that the proliferation of the internet, while massively increasing potential customers, actually made it much tougher to recruit models. In those early days of WH, he seemed to have hordes of guys turning up for shoots daily, who would in turn invite their friends and brothers and teammates and fellow soldiers etc to audition and make some easy money. The internet wasn't mainstream yet - this was long before Youtube, and even longer still before smartphones - and I'd hazard that most of these guys did it because the shoots were only being published on this obscure geeky internet thing - no one they knew was ever going to see it. Today, obviously, it's a completely different ballgame.
And now the rise of Only Fans and suchlike further compounds the difficulty of recruiting models. When the studio had exclusive use of filming equipment and distribution, it had total power. Now that every budding pornstar has the equipment (smartphone) and means of distribution (wifi/4G) they can cut out the middle man and keep all the revenue for themselves.
Ultimately there's just no longer the same money to be made from professional porn. You can't subsidise costs by throwing some scenes on a DVD and selling thousands of them around the world, as WH used to do, because who buys DVDs any more? And the rampant spread of tube sites and torrent sites means your content is being distributed for free much more easily than in 2004 or whatever, meaning fewer paying subscribers. Which then affects content.
I do actually think the site today is faring pretty well compared to most of its long-running peers - lots of content still, if not nearly as much as before, and still the occasional stunning guy - but I doubt it'll ever return to the quality of its heyday. It's a real shame they removed access to all that classic content. It might be gone for good.
