When I was the Parts Department Manager at Kato USA I lobbied for what I felt would be a reasonable level of parts to last between production runs using the parts.
The North American need and use for parts is totally different than the Japanese experience....there, for the most part, N Scale trains are consumable goods with a limited lifetime....kids outgrow their trains and typical homes have no room to “keep stuff’. They sell “assemblies” including complete decorated bodies which seem to be aimed to repair broken toys and not for hobbyists.
By contrast, many of us have most everything we’ve purchased for our adult hobby and like to keep it running.....even if it is a 40 year old locomotive. We actually can wear out our trains through heavy use. Without permanent layouts wear is not an issue.
Charlie Vlk