As others have said, the term "touring" was around first. As to why they started using "bike packing" , it probably has as much to do with marketing and opening up a new stream of revenue to the industry.
aahh..yep.
The largest/easiest population of consumers to sell bike stuff to is the group that already has bike stuff. The problem is, if they already have the bike stuff you're trying to sell..well..then they won't buy more bike stuff. The key is to carve out(create, invent, redefine, market into existence even if it doesn't exist) a block of new bike stuff that the consumers don't have..and being good consumers, they'll then line up to buy new bike stuff to add to their pile of old bike stuff.
rinse..
repeat..