Just thought I'd add my thoughts..........
Firstly there are not actually that many people I see in Cornwall actually doing a proper bottom turn. Sure a lot of people can turn back up the wave, but not really off the bottom IMO. Clearly the most important thing is practice, but I think one important thing to note is that most people don't appear to me to drop far enough in front of the wave. You can't do a solid bottom turn if you're turning when you're still half way up the wave!
Next time your out in the water look how far out the guys who actually rip go in front of the wave in order to do that crucial bottom turn. Or in fact just watch a video carefully.
It may feel like you're going a long way out in front of the wave, but chances it's not far enough.
If you're angling on take off then chances are you're not about to go straight into a bottom turn.
I think the main problem is, is that it's actively trying to do the opposite of what you have been doing since you started going along on a wave, i.e. you try and avoid the flats. But you must try to just drop straight down the wave, right to the bottom and then do your turn. If the wave is too fat then turn halfway up the face and do a cutback. Easy as that!
Everyone seems to think that the wave will run off if you don't angle straight away on take off, but the reality is that you will generate more speed by bottom turning as you will actually be in the pocket (obviously doesn't apply if the wave is actually running off in front of you, which is unfortunately often the case in Cornwall!).
Well I could go on, but I think I've said quite enough.