the 1990 GT has reverse. It's probably the first 3 passenger ski available ever, and it had reverse.
Reverse isn't something that needed to be addressed... it is on some... and not on others. A small high speed ski doesn't need it... or if the manufacture was trying to keep the price down... they would leave features off.
Now... I think every SeaDoo made has reverse. (just in the last few years) This is because of the safety advocates... and all that's done is bring the price of a base ski into the $9k range.