For what they need to do, the factory shocks are more than adequate. A bike like a ours is sold to people of many sizes and requirements. Large people who want to ride aggressively, smaller people who want to commute back and forth to work, passengers, luggage and camping gear. Smooth roads, and terrible roads. The interstate and canyons. The factory has to find some kind of happy medium, and not spend a ton of money doing it.
Factory marketing types know that there is a large aftermarket for suspension upgrades with a range of performance and price points that will meet most riders requirements. It makes no sense to the factory to add more cost to an already expensive machine to include a rear shock that many owners will replace as soon as possible. A good middle of the road unit that will last 4-5 years is all the bike needs to get off the showroom floor. Then the owner can replace it with something that makes his a$$ happier.
