RE: Customer loyalty and OS parts supply
Basically, once an engine has been out of production for more than five years, worldwide parts demand falls to such a low level that it is not economical for O.S. to keep them in production. The worldwide demand for old parts is so low that even if O.S. took orders for a full year and then made only those parts, the price would have to be at such a level that most of those buyers would back out. Experience over the years has shown that it's just not worth it. The demand is just too low for O.S. to make parts for those older engines.
Also, even though there appears to be a "lot" of demand for the older "Pattern"-type engines, the number actually needed is very, very small when the worldwide market is considered.