I can't tell you the number of times I've gotten passionate/excited about something and shared it with someone who might care, only to have them say "that's nice" and go about their business.
More often than not that's the case.
Sometimes, of course, you get excited, you share your passion with someone and that kickstarts them into high gear as well. That feels really good.
I am not sure what the mechanisms are for starting a fire under someone.
I suppose it has something to do with their interest in the subject, certainly, but perhaps more importantly it must be timing.
Yes, I suppose, timing is everything. And how hard it must be to find a person interested in the same subject as you, ready to receive your input about the very subject they are interested in at the same time.
Passion is contagious but only through a very narrow window of time and circumstances.
Passionate today, not interested tomorrow.