Interesting development

I tend to follow the sales of various LP’s on Ebay. Recently, i have noticed that the price of many of them seems to have skyrocketed! For example, many of the Mobile Fidelity albums have sold for prices that are two-four times more than what they were when new! This is a new development, as only recently, say in the last six months, the same LP’s were selling at or below their original retail price, no more! The recent MFSL reissues of the  Miles Davis LP’s are a good example...some of them sat on the various sites that sold them new for years at the same price, or even slightly below...now we see these very same albums going for up to four times what they originally sold for..
Same goes for several of the Analogue Productions reissues..what’s up??