Are you asking why it is so expensive to buy on the resale market or just rent the week for a week's stay on RedWeek?
If you are asking about buying I can tell you that we bought 2 regular Platinum weeks 10+ years ago. Although I am persistent enough to somehow always secure July or August reservations (which is what everyone seems to want in a 7 month Platinum season), I eventually decided that it was worth it to just buy a fixed 4th of July week and be able to pretty much guarantee the first 3 weeks in July. I used to get 2 summer weeks but it wasn't always the week I wanted - I would try at 13 months out week after week and then at 12 months out online and via phone... I'd make it work but it was stressful and a huge pain. Is that alone worth a premium of almost 200% (cost is almost triple)? Maybe not, but there is also another reason to do it...
A regular Platinum weeks converts to 3475 points. The 4th of July week converts to 5300 points. While a resale purchase is not eligible to be enrolled, we all know that if you ever consider making a developer purchase it is always good to have a few resale weeks in your back pocket since they will offer to enroll those resale weeks. I haven't done deep research on this, but I suspect there are few, if any, weeks in the points system that offer a better Points/MF ratio (MF + taxes, which are paid to county separately, are about $1600/year). Before we got the week 26, we were at a presentation at NCV and were offered a "combo" deal to buy a PP Week 52 from the developer and 3000 DC points. Week 52 is worth about 4600 points and has a lower rental value so I told them that, while it was a good sales pitch, we'll get a week 26 on the resale market for less than their price for the week 52 and see them again in a couple of years

. Of course they said that deal is gone the moment we walk out... But for anyone considering just the points value for a potential enrollment down the road without caring about summer week reservations, the premium on the resale market for a Week 52 over a regular Platinum week is much lower, so that may be a better option.
As for rental value, it does rent a for a 15-20% premium over a regular summer week ($3000+ vs $2500+), and that extra ~$500 or so in rent is by itself a 4%-5% return on the extra $10K-$12K you pay up front above the price of regular Platinum. Remember that the upfront purchase cost is not automatically a huge capital loss like with a developer purchase - I remember that pre-2010 a 4th of July week was around $15K on eBay. I kick myself to this day for not getting that one, especially after the 2010 events... So in the past 11+ years it has actually maintained its value and maybe even appreciated slightly in value on the resale market (I think they go for $17K-$18K today) despite maintenance fees increasing by over 50% during that time. That's in contrast to Platinum weeks that fell in value from $11$K-$12K pre-2010 to $6.5K-$7K today. And for those who can convert to points, the rental value of the 5300 points is actually higher than the rental value of the 4th of July week.