Maybe a long time ago, servicable components made some sense, but when the progress of technology accelerated from the 60's and later, people would rather just "retire" the worn out component and move on to the next newest, hopefully better thing to either stay competitive as a racer or to just satisfy that inner techy gearhead geekness that many of us have to some degree.
For example, I really doubt if any significant percentage of all the Mavic 851 SSC and 810 RDs made were ever overhauled by their owners with replacement parts to keep them going. And that would most likely be similar to other "rebuildable" RDs and FDs. from other makers. Like everything else, things are now mostly plug and play.....then throw away..........or sell to some desperate C&Ver guy at eBay.....
JMOs

Chombi