Even if you limited GC to when owners are present, you're still going to have people renting. They just need to make a two-night reservation for themselves. Sure, that increases their cost, but they can just increase the cost of the reservation. There are fewer people renting, so prices are going up anyway. Until Wyndham verifies that the owner actually checked in, renters can use this to get around the rules. Sure, the concierge can ask if they know the owner (which they do now), but the seller can just coach the buyers and tell them what to say. Sellers always find a way.
Eliminating GC entirely is not an option either. Owners want to send family on vacation without making them financially liable for their timeshare. Not to mention, adding them gives them access to their account. As
@HitchHiker71 said, we have suggested a friends and family listed multiple times over the years. This would help, but still wouldn't eliminate the need for GC. Wyndham would likely limit it to a handful of names and would limit how often you can change it. Maybe you want to send someone on their honeymoon that's not on your list. Maybe a family in your church group has to get medical treatment out of state and needs a place to stay. I've seen both these scenarios. I myself sent my cousin on his honeymoon in Rio Mar.
I am not a fan of people renting for profit, but I am not onboard with eliminating GC entirely. There is no cookie cutter solution that is going to fix the problem without hurting the owner who is following the rules.