They take longer to clean only because they are typically older than most other bikes, and often times haven't been maintained, so the parts are that much dirtier and that much worse for wear.

Flushing out a 30 year old rear derailleur can take time. soak it, rinse off and rub grime/grease/dirt. soak more to continue to break down the junk. rinse and rub off grime. then work on the interior to get the grit out of the hinges. rinse. work it out. rinse. etc etc.

Perhaps so many others here just encounter bikes that are in a rougher starting point than you? Or you work amazingly fast? Or others have a different standard of clean and reconditioned than you?

If you completely break the RD down to its parts, soak and clean them, then rebuild the RD, that will suck up a good % of the time you list for rebuilding an entire bike.
How about a rear wheel- removing the freewheel, cleaning the freewheel of all dirt rust grime and grit, breaking the hub down to all the washers bearings cones and axle, cleaning all the hub components, cleaning out the hub of all old grease, then repacking the bearings and reinstalling the components should take another good % of that time you mention.

So just cleaning and servicing the RD and rear hub could take a couple hours, and that isn't even adding in the time to clean the rim and spokes.
Again, we may just have different standards of reconditioned. Or perhaps you are speaking of building up a bike once all the parts are in front of you in buildable condition.



This has gotten far off original topic- apologies to the posters in the thread!