I don't think anyone is ignoring it, it's just an obvious common-sense thing that most people have an idea of the general guidelines about.
Ask Disney what they think about someone coming in and knocking off one of their limited edition or even regular but long-NLA items. It's a major no-no and they have no sense of humor about it.
Now in the pinball/modding community, things are a lot more relaxed, so I would think that if a mod was long out of production (4 years? 5? Basically a long time) and you had the ability to do a copy or something very similar well and wanted to tread that road instead of exploring your own new and creative ideas, the LEAST you could do is contact the original modder for their blessing. Maybe they're out of mods and would be happy to let you continue. Maybe they would be offended and say no. Whatever the outcome, that would be the very least I would expect for that situation.