It was never practical to take photos of live butterflies with film cameras. Although the Digital Camera was invented in 1975, taking photos of live butterflies with Digital Cameras didn't become popular until around the year 2000. So, ever since around the year 2000 it has been "POLITICALLY CORRECT" to take photos of live butterflies with Digital Cameras rather than collect dead butterflies, which was done for hundreds of years prior to the year 2000.
However, taking photos of live butterflies has BIG disadvantages:
1) Live butterflies don't always open their wings and pose for you.
2) It is EXTREMELY difficult to take photos of live butterflies which:
A) Are on islands or other remote places which are difficult to get to(e.g. Maluku Islands of Indonesia).
B) Are Rare(e.g. most Birdwings).
C) Fly very fast(e.g. Agrias).
D) Fly only at the tops of the trees in the Rain Forests(e.g Antimachus).
3) When you take photos of live butterflies you are usually restricted to the geographic area where you live. That's because traveling all over the world to take photos of live butterflies would require an INCREDIBLE AMOUNT OF TIME AND MONEY.
ALL of these problems disappear when you take photos from a collection of dead butterflies. Remember that butterflies usually only live about 2 weeks and after they're dead they can easily be collected and distributed. Over 90% of all of the beautiful butterflies in the World come from the Rain Forests in the Far East, Africa and South America. The people who live in these Rain Forests are usually indigenous people who are VERY POOR. So, the money that these people make from selling dead butterflies is one of the main reasons they don't cut/burn down their trees for agricultural purposes or for cattle grazing.
Some other advantages of taking photos of dead Butterflies instead of live butterflies: