Metal straps on strut with a metal bolt creates a conductive loop around the conductors. The loop is an inductor that adds impedance to the circuit. It is like those little doughnuts of magnetic material that are fastened on the power supply cords for our laptops, digital cameras and USB devices. The inductance helps mitigate surge currents, especially high frequency ones.
The telecom cables may be carrying some high frequency signals that are affected or attenuated by the inductive loop of the conduit straps. Using plastic bolts breaks the conductive loop.
The specifications for the main signal grounds in telephone Central Offices used to require the braided ground cable to be run in PVC with PVC bolts, etc to avoid the inductive loops.
Some lightning protection standards require the same thing because that steep-fronted lightning voltage surge acts like a high frequency signal. Any inductive loop adds some impedance to the ground path. A 1/4 ohm impedance at 20,000 amps lightning current results in a 5 kV voltage drop.
But in the grounding application only one conductor is going through the loop; the return conductor (the earth) is outside the loop. With the telephone pairs, both the conductors are inside the loop so I don't see there being that much of an effect since the net current is theoretically zero.
I wonder if the ground cable standard got misapplied to the telecom cables.
ower cable in close proximity to an instrument cable.,large metal structures also may give some trouble but shielding is usually adequate.