Yes, they do encourage animal intervention too, as well as discourage it. I'm not saying they don't.

I'm suggesting a primary purpose for trich's... a reason for their development in the first place... or second place... doesn't matter.

What does matter is that there is enough evidence to suggest that trich's also magnify light. To my mind, the immediate survival of the plant itself would come first... else how would it produce the seed in the first place?