For example, a building built in 1960 had analog phone lines. Then in the 80s network lines were added. Then in the 90s - 00s more and more and more network were added.
Then in the 2010-2020's we're starting to wind back down. Removing switches and racks that used to be fully populated with CAT5 which are now mostly empty. The end devices that needed these runs are now running on WiFi.
I've been in many, many buildings for cabling issues. While I generally agree with your assessment of "run more everything" I think this could be taken out of hand for a lot of smaller IT departments who aren't capable of using more advanced methods of network building. Like subnetting, VLAN trunking, or redundant links.
Why would you need to learn about these things if you've got 3 or 4 more pairs of fiber hanging down? Then you have a situation that I've seen before, where you have 2 fiber runs carrying flat networks right next to each other with just a couple of IP phones on each one.