1. The team was constantly being chopped and changed.
2. Lara was constantly fighting with the board over the quality of local pitches, player selection and player pay, leading to several fines, reprimands and loss of captaincies.
3. In the 1990s, Hooper, Chanderpaul and Jimmy Adams were the only consistently selected batsmen other than Lara. Adams took a hit to the head, became a scared batsman, and lost his form in the mid 90s. Hooper was always unreliable and Chanderpaul only became a great after Lara left (it took Chanderpaul almost a decade to learn how to make a ton, due to a problem with a floating bone in his foot, which he had removed late in life).
4. No consistently selected openers. Openers are the bedrock of a test innings, and since the retirement of Greenidge and Haynes, the West Indies have never had consistently selected, decent openers. Sherwin Campbell (mediocre) and Gayle (decent) were their best, non of whom had stable partners.
5. Sarwan and Gayle only became reliable and somewhat mature after Lara left.
6. Once Ambrose and Walsh hung up their boots, the WI had no good pacers. The next wave of decent pacers (Roach, Taylor, Gabriel), coincided with the WICB taking a more active role in creating and training pacers (setting up High Performance Clinics etc).
7. The WICB fired Rohan Kanhai as coach, a masterful player, believing that the West Indies didn't need a coach. The Windies' fall coincides with his removal and the arrival of Steve Waugh's first tour to the Caribbean.
8. Ritchie Richardson was the last reliable WI captain, but he was a political pick by Viv Richards, and set in stone a kind of favoritism and unprofessionalism that carried on for decades. Whilst other teams were becoming well-oiled machines, with modern training methods, routines and technologies (video replay etc), the West Indies relied on raw talent, intra-island cliques and friendly favors.
9. No money and poor organizational bodies.
10. Lara went from poverty to a rich kid with no dad. While someone like Tendulkar had large support and familial/traditional networks to stabilize his transition from poverty to icon, Lara handled it all alone, and went the other way. He burned out, partied hard, and lost interest in cricket (the famous Lara quote, "cricket is ruining my life"). Only in the early 2000s would he, monk-like, sort his head out and resurrect himself.
11. Too many good bowlers. Warne, Donald, McGrath, Kumble, Murali, Gough, Flintoff, Akram, Younis etc etc. West Indies' fall coincides with other teams fielding some of their strongest attacks.