PL home games don't result in additional loyalty points as such, apart from the 30 points for renewing given at the start of the season, so in your suggestion the club would need to remove a portion of those 30 points, which would be controversial.
Maybe a better way would be to treat attendance at PL games in the same way as attendance at Cup games - instead of the bulk 30 points at the start of the season, you build up points if your ST is scanned at the gate, but if you sell it on the exchange, or pass it on via ticket share, then you don't get any. Again, I suspect that wouldn't be popular.
Shouldn't forget that tickets being listed on the exchange is often the only way a lot of Members can get tickets for games.
Of course, there is an assumption being made that all these missing ST holders are ones who would improve the atmosphere were they to attend, which I doubt would always be the case.