It's mainly the difficulty of getting sufficient information to people to let them understand what they are seeing. Field guides are generally detailed but you

It's mainly the difficulty of getting sufficient information to people to let them understand what they are seeing. Field guides are generally detailed but you need to have some identification skills and know how the field guide is organised. The general guides cannot provide sufficient coverage so you need one for birds, one for mushrooms, one for trees, one for flowers, etc. etc. A phone app solves a lot of that. The additional advantage of phone app is that allows casual contact (assuming people are motivated enough to install it) so if someone comes across a flower or tree with fruit they have enough information to at least identify it and perhaps learn some more about it. That's a huge step forward compared to today.