The ends of a 1/2 wave dipole are high impedance and can have very high voltages on them. If you were to have bare wire attached to rope and the rope gets wet, it can change the characteristics of the antenna. You can also start a fire with enough power and the right circumstances.
Its a good idea to use an adequate RF and high voltage insulator on the dipole ends and mfrs of these antennas have no way of knowing how you will use them so they come with insulators.
Just my 2c
As pcrguy points out, there is high voltage at the ends of a dipole.
But, I've actually gotten away with using plain yellow nylon rope. I had a 40 meter dipole up for several years. The rope at the ends was supposed to be temporary while I tested it, but it worked OK rain or shine so it stayed as it was much longer than I anticipated.
Right now, all I have is an 80 meter inverted vee in place. I am using proper insulators between the ends of the antenna and the support ropes.