The point is that the bike is a solved technology, the best materials, geometries and systems for all the various applications have been figured out, but up until the late 90's there was still plenty of actual innovation and experimentation going on, lessons were still being learned, especially within the realm of the then quite new and exciting 'mountain biking'.
Once they started to perfect the various elements and as bike designs became more refined and specialized the industry's focus switched to making things more cheaply and, more noticeably, with shorter life spans. As recreational cycling reached its zenith and as the global economy opened up to China with its cheaper steel, aluminium and carbon and super low cost mass production something important was lost forever, the age of mad genii competing and cooperating with one another as they collectively pushed the envelope of what was possible was over, the multinational corporations now held sway. God tier brands were being swallowed up, reduced to the status of a sticker on an otherwise unremarkable cookie cutter bicycle built by slaves with the cheapest possible materials churned out by the thousands.
Many of the mtb components from the mid 1980's to the mid 1990's were significantly over built, as were the frames, that's why they are still going strong today, it's why people prize them, even mid range bikes from that era are revered, especially when compared with similarly priced equivalents of today with their perfectly executed built in obsolescence, now even frames are being reduced to the status of a consumable.
1998 was the beginning of the end when viewed in those terms, of course many great bikes came out since then and continue to be built today, and innovations occasionally crop up, just nowhere near on the same level, pre 1998 was a golden age in the same way the age of steam was a golden age for trains, just as the internal combustion engine will be similarly viewed for cars in the not too distant future.
