Because Warne's statistics do not come close to comparing to the likes of Hadlee, Holding, Ambrose, Marshall, Chatfield, Pollock, Muralitharan, McGrath, Imran and Wasim. No doubt you'll point to Warne's World Cup record, but even it isn't as good as some of the bowlers I have listed.
If only Joel Garner had played two more games then in my mind he would be undoubtedly the best ODI bowler of all-time, quite comfortably. 100 games is the minimum judgement of players for me, which may be a little high, but I'll look at reviewing it.