There's often roofing nails and broken glass and other debris way over on the shoulder too that can cause flats on a bike. I don't ride in that stuff for the same reason that you wouldn't want to drive in it. And bicycle tires on a road bike puncture a lot easier than a car or truck tire does.
If folks are riding side by side on a two lane road, they sure oughta get single file when a car or truck is coming...and if it's a busy two lane road, they shouldn't be riding side by side at all.
Try riding AGINEST traffic and see if you move over if there is so much room
