FWIW: I've been a ref at the last 4 Pan Ams and have competed in every Pan Ams since 1999. For as long as I started paying attention to such things, they've had a rules meeting/seminar the day before the Pan Ams where the legality/illegality of leglocks (and everything else) has always been clearly explained.
Reaping of the leg on a straight achilles has been illegal as long as I can remember. It is not the referee's job to explain the rules during the competition. The coaches should attend the rules meetings and inform their students.
I have DQ'ed blue belts and purple belts for doing illegal footlocks, kneebars, etc. and it had northing to do with anyone's country of origin or BJJ team.
IIRC, kneebars used to be legal for belts below brown, but they had A LOT of knee injuries in Brazil and the decided to restrict them to brown and black.
Regarding the general issue of BJJ and leglocks: It is a generalization to say they are not taught in BJJ academies. I teach them in mine and always explain to my students that some are not legal in all tournaments and they need to know the rules before they compete so they don't get DQ'ed. Also, I explain that even if certain leglocks are illegal in certain competitions, it is still important for them to learn them. Finally, we compete in a lot of no-gi competitions and more leglocks are allowed there.