What's the good reason? There hasn't been a premiere athlete who has used the straddle technique since the 70's. Mathematically it's possible to reach 0 center of gravity using the flop or straddle and it's possible with either to reach -0 COG so neither limits the jumper except for preference. One mathematician believes that the high jump will remain stagnant until the straddle makes a comeback. I coach MS track and have taught both. I've taught kids the straddle only to have them switched to the flop by the HS coach. Some kids love jumping but just don't do well with the flop.