What the heck is up with 8-3/4" rearends?

Prices for all rear ends are high. I also have a Jeep Wrangler and it is not uncommon to pay that much for a dana44. I am lucky enough that I bought my a body rear end from a wrecking yard in 1992 for 125 brake to brake. It still resides in my 67 Dart. My 69 Dart and 68 Satellite were both born with 8 3/4 rear ends. the limited slip iny satellite came out of a 1973 Dodge Van I used to own. The 3.9 to 1 gears came out if a 1965 A 100 I found in the wrecking yard 15 years ago.