can someone tell me what's so good about XLR?
Very good question!
There are a couple of reasons why XLR scores over a TRS plug, and all of them are practical, not because "XLR is better sounding".
The reason XLR was developed in the first place was because on a TRS plug, when you connect or disconnect it, each part of the plug (tip, ring and sleeve) pass through the jack at different times and this can cause a loud system-damaging pop if you do not mute the input/output first. With an XLR, you are connecting the signal and ground at the same time; hence no nasty pop.
Also, an XLR plug locks into place so that accidental tugs do not pull the cable loose.
The 3rd reason is because an XLR cable/plug can carry both signal and voltage at the same time.