Probably because most SLF can't figure out why you're asking to see the boarding pass stub? it's never explained clearly that you as a responsible crew member need to verify they are getting on the correct aircraft.
I once overheard a gruff pax mumbling 'I didn't need her to tell me what
f
ing seat I'm in I can read numbers me'self'
Respect to you for doing a damn challanging job
