To me it's all quite simple really. Even the late 90's trance was much more commercial and formulaic compared to the early 90's. And, that was due to the popularity of clubs like Gatecrasher, Cream, huge number of mix CD's out on the market, radio shows where DJs played mostly trance, large legal festivals, etc. A lot of people who listened to trance in the early 90's complained that trance was dead by the late 90's and hated that more modern sound.
Commercial forces and $$ drove many producers to make a more cheesy formulaic sound. Ferry Corsten was a pioneer of this type of trance, and whether you like him or not there's no denying that 99.9% of his late 90's sound had similar structure: build up, breakdown, massive hand in the air riff, etc. And this was the kind of trance that packed out clubs and festivals, sold mix CDs by the ton and catapulted trance records like Gouryella, etc. into the pop charts.
Now in the 2000's this all went next level when Tiesto played his first solo gig in May 2003. Producers and DJs realised how much more money they could make by putting on massive solo stadium shows. After Tiesto, other producers steadily followed suit, most notably Armin and Above & Beyond. The latter two acts became particularly powerful players in the scene due to Armin and his company buying up so many other smaller trance labels in the digital era. A&B obviously had Anjunabeats, etc. and the radio shows increased their audience and popularity and the money flowed in steadily. The music itself became more and more commercial sounding to please the ever growing crowds of followers. Pandering to the most common denominator and all that.
Now, this was the kind of trance a lot of the newer producers grew up with so they followed suit and made the kind of trance that would be played by their heroes. This was no longer trance in my opinion, it gradually morphed into electronic pop music. EDM explosion was just a natural consequence of the mass commercialization of the whole dance music scene. Play to ever bigger crowds, make ever more commercial, bleepy music to cater to shorter attention spans and keep everyone happy by giving them the type of music they could easily "get". I.e. pop music.
Now this pop-trance is far away from the type of trance with quality track structure, the feel of a journey, melodies and atmosphere. However, that's not to say that quality trance ever died. I strongly disagree with anyone who says that trance died after this year or that or that the quality of music decreased. In fact, I think that real trance has only become better over the years. There are still lots of producers, DJs and labels that release good quality trance. It's just that this is far out numbered by the commercial trance which gives the impression that there in no quality music out there and trance is dead and an irrelevance.
The scene nowadays is a lot more fragmented than ever before. Everyone and their dog has their own radio show, new releases come like a deluge due to DAWs and a huge number of record labels. All it takes is a little bit of research, perseverance and digging around to find the quality stuff. And, it is well worth it.