Ergh, prices. I don't know. I've noticed it with the Glowing Magics especially. I've seen some go for stupid money lately. One sold with her card and stuff here for £65. Well, good luck to the seller. There was a variant Brightglow recently who I passed on because she'd been restored so it wasn't a guarantee the variation was authentic, but she was also quite expensive. Maybe because of the variation but...*shrug*.
But then...brace yourself for old person memories coming through now.
Which ponies are expensive has largely changed. Some haven't (Mimic, Rapunzel), they've just got more expensive with inflation and the theory our generation now has more disposable income (chance would be a fine thing!). But I remember the first baby AJ on ebay sold for $300. I think she's around $20-40 now at best.
I come from the backdrop of carbooting most of my ponies in the middle nineties and trading for the rest in the exchange rate of the time - where UK and European ponies were very expensive due to the limited online supply. And now it's fairer and more balanced which is actually good. But it's not good that certain ponies and sets have gone up. Glowing Magics seem to be one of those.
As for the Princess ponies, their accessories have always been more expensive than them, but the second set had a limited release geographically compared to the first. That may feed into it. And it also may be more people trying to buy domestically because of all the problems this year.
But...
Summer is the cheapest time to buy ponies