I get it. The sequence of events seems very analogous to a Rube Goldberg machine, and one would conclude if the sequence of events didn't go as planned the parasite would have been doomed.
My theory is the parasite community for that species can survive other ways just fine, but has stumbled across a scenario that serendipidously gives it an extra boost at the change of reproducing.
I would imagine that most species that benefit from these complex interactions tend to have left-over backups for survival and reproduction. When species over-adapt to specific scenarios, it seems likely they'd become to susceptible extinction or their populations would be periodically thinned out.
