315 restoration motivation?

There has always been a lot of dreaming about restoring a big variety of engines to operating condition.

In the case of the 315, it has been done thanks to a huge effort by a lot of dedicated and very talented volunteers.

I'm wondering what factors were the main incentives to undertake the restoration, and whether those factors are present for any other currently non-operational engines anywhere.

In other words, what went through the minds of the folks that decided to dedicate a large part of their lives to doing this?

I also wonder in the case of any other non-operating engines whether such a talented group could be gathered for that type of an effort?