I really like the points you made here, most old dead projects have most of these factors affecting them. Imagine when members of a community supporting a project completely lose interest in it due to declining coin price or absence of updates or development, the project will crumble eventually. Also, there is a vital point you missed which is lack of funding to continue with the project. Some few genuine projects which lack funding and hence can't keep paying workers, or keep up with developing product, marketing etc, still go under the radar. Truth about most altcoin projects is that they won't last long term before they go extinct or exit scam, just very few last the test of time.