Yes, they invested money in Rocket Rods, but that doesn't mean everything they invest money in now will fail.
Disney buys buses all the time from a company that specializes in manufacturing buses. That company sells buses to a lot of other people besides Disney too. Disney relies on them to be experts in designing and building buses. The gondolas are a much more similar situation to that. The company they are buying the system from has experience building similar systems around the world. Disney can rely on their experience and expertise to help decide what's the best option.
A fan may be a doable option. The problem with the AC is charging the battery. The gondola is only in the station for a minute or 2 at most which isn't a lot of time to charge the battery. The system in Macau has AC powered that way, but it has had mixed reviews.