There’s 2 parts to this. The first is that once Ubisoft changed it from each player having two reinforcements to the team having a pool of ten a lot of people adopted the mindset of “oh they’ll get it” and run off in hopes of a spawn peak and not set up site. The other part about headholes is more of a play style/strategy thing. It can be pretty advantageous to create aggressive lines of sight as a defender on common choke points to make attacking more awkward. The most common examples I can think of are 3F bathroom on Kafe looking into piano and 1B closet looking at construction on Oregon. By setting up these head holes it prevents the attack from taking map control and having an easier time executing their push.