Kay;
That fuel supply line was friction fit only by Volvo to begin with, without ANYTHING else securing it into place, and I agree it doesn't need anything...so if someone added a nylon wire tie, which are typically rated to (105Deg C) 94V0* (self extinguishing nylon), to snug this line onto the fitting just a bit, it wouldn't bother me as much as it apparently bothers you...
Cheers
* Reference:
https://www.professionalplastics.com...onsForPlastics