I always assumed he was too lazy and failed to realize the benefits of it, kind like most people know they should exercise and eat healthy but they don't.
Joseph just couldn't be bothered.
DIO stopped The World from punching Joseph due to Joseph having infused himself (as his stand) with Ripple, so it's very likely that Stands do conduct Ripple.
Plus Ripple works in humans which makes it useful to attack stand users.
well, it could be argued that the contact would come from Hermit Purple being infused with Ripple. the Ripple alone wouldn't work but it would through a Stand. we never see this in action since there was no other Vampire Stand user that fought against a Ripple Stand user so it's all speculation in the end.
also, at the time they probably wanted to get rid of the Ripple fast since it was "boring" and the Stands were the new hotness. it's funny since it's kind of the opposite for many people who begin watching Jojo and then have a hard time in the transition because Ripple is more unique nowadays when a ton of mangas/animes use Stand-like powers. this is interesting because, if Jojo was made today, maybe the Ripple would have continued longer but then, if Jojo wasn't made when it was made, not many series would have been inspired by it and the ripple wouldn't look unique.