First of all, most of the juice in the worst-of revcon comes from the worst-of component, so a single asset down-and-in put will not be equivalent. Second of all, variation margin on an OTC product like this would be rather high, so you are not saving that much cash. Third of all, given how competitive the space is, when you buying a structured note, you are usually get a nice funding pickup. There are also tax considerations and many other things.
PS. pure N-worst-of forward notes were very popular with PWM accounts for a while. if you can pick stocks, the structure makes a fair bit of sense when correlation is low and volatility is high