In addition to limited access or a quick install turnaround the installer may not want to install in a wardrobe due to lack of ventilation?  Although it might be an unused cupboard now, once it has coats and other clothing in it it could pose a fire risk especially if a hanging coat or similar covers the vents of the ONT.

The copper connection argument annoys me.  We recently had fibre installed and they were good about where the ONT was installed which happened to be around the TV area.  One of the guys was confused as to why I suggested behind the TV when the phone jack was in the hallway.  Although we chose to retain our landline (for now) he was adamant it needed to be installed next to the jack point.  I knew our ISP configures VOIP on a POTS input on the ONT directly so totally negated the need for the jack point.

When the guy finished I found another unmarked and unpowered box screwed to the wall alongside the ONT that I hadn't seen or heard of anyone else having installed.  It was basically a new copper master junction box so the 'copper network' of the house could all connect to the ONT if required in the future.  Great... except they knew the house only had one jack point but he said they don't get paid if they don't install the box.