First my thanks to Mike, Steve, those preserving our heritage, and those having morals.
Two points I'd like to add are legacy and design changes. I recently became the caretaker of the Dave Gumz 4-6-0 built from castings and drawings by Warren Weston. Sadly the locomotive did not come with drawings and maintenance will be required. Fortunately a friend from the Golden Gate Live Steamers (GGLS) gave me two boxes filled with Modeltec magazines and said they're in there. Dig, dig, dig and I found 25 issues discussing the build with many drawings. I also found an advertisement for Warren and I gave him a call. Turns out he had had a stroke, the family downsized, and apparently all the drawings and patterns were tossed. Groan... (ref. thread: Dave Gumz' 4-6-0 4-3/4" Narrow Gauge).
Second is design changes. A few years back I purchased a partially built Little Engines 0-4-0T from an estate; Burt Miller had begun construction on it around the late 1980s. The piping was beyond my ability and I took it to a "locomotive works" to be completed (that's another story). The builder followed the supplied throttle drawings but then discovered the 0-4-0T had a smaller diameter smoke box. He said that's okay, he'd shorten pipes and make it fit. The problem with that idea was the throttle could only be full open or full closed. One good thing was that the builder had a good rapport with Mike of Little Engines who basically said, "Oh yeah, there's a new drawing" (2002 vs. 1982). Fortunately Mike sent the drawing and third time was a charm. Once again, thank you Mike! Fortunately I made sure to pick up the drawings when I took delivery.
There are those of us old enough to remember Napster and those having morals. An acquaintance at work used to call me a fool for spending a $1/song on iTunes rather than stealing it with Napster. The legal system caught up with Napster but that took a lot of money. Companies like Little Engines and Allen Models possibly don't have the deep pockets like Sony, et. al. Morals & ethics, something a few need to learn about.
"History makes you smart, heritage makes you proud", "To Infinity & Beyond!" and have a safe & prosperous new year!