Why still-in-pBook-print-run-but-still-"backlist" ebooks should be cheaper than recently-printed-ebooks:
https://www.mobileread.com/forums/sho...4&postcount=77
If the book has maintained its popularity all this time, then publishing the backlist isn't the risk that backlist publishing often is. The publisher doesn't need to spend money marketing the book or reminding people that it exists -- the market already exists and is known.
Because the publisher has to invest less marketing, they can bring the price down relative to other, lesser known works. The publisher isn't taking a risk that they'll lose their eBook conversion investment, and thus they can bring down the price to lower than BOTH comparable ebooks AND the print run of the same book.
By keeping the price artificially high (i.e., to capitalize on the LESS marketing for MORE profit), they lose sales to the existing backlog of used paper copies of the same book. (Which will be HUGE if the pBook has been in such high demand that it's been in print all these years -- there will be tons of available copies).