One thing is certain: people do love and pick them as assiduously as the deer, and the riparian habitats where these are found are optimal spots for all sorts of human activities from towns and farms to ranches and ranchettes...we are undoubtedly the primary cause for the rarity of Lilium philadelphicum var. andinum.
Incidentally, I took the first picture of Lilium philadelphicum on June 14 last year. This year they have been in full bloom a full three weeks earlier. That's the sort of year it's been. There are coarse lilies (mostly hybrids) and those with great tenacity. But most are delicate as their name implies, and it behooves us to cherish and encourage their numbers in gardens and the wild: that's our choice as humans. "The solution to pollution is dilution" may not be so very true in the closed ecosystem of our shrinking world. But I do aver that the salvation of our nation's showy rare plants lies in propagation and education.