I don't think it is so much of the gym being extremely difficult, but more that it is extremely time consuming. I haven't even attempted Tene's course because it would take ages for me to complete, and honestly, I'm just too lazy to put in 2-3 hours on a gym course. Also, most Johto courses are like this, which makes it even longer to get badges. So with people taking forever to get badges or just not wanting them at all, they can't challenge the Johto Elite 4, so being a Johto Elite is on low demand, since there are almost never challenges. As for the keep inventory idea, I dislike it. As an Elite, I use potions during fights, which take up a lot of inventory space. That added to enough sets for 4 or 5 fights, weapons, and OP apples, would just be too much. Though I think it would add to the Pokemon theme, I don't think it'd be very fun for those challenging the Elite 4. Those are just my thoughts on it.