I'm new here but I have already read a few "rules question" threads and see that the OP is noting something that does happen. A few posts have the actual answer and cite the rule number. Then there is a lot of "around here." There seems to be some additional challenge by having varied governing bodies, that create "it depends" answers.
It probably is healthy for a sport that participants know and apply the rules accurately and consistently. For that reason, limiting "around here" rules might be best. But we would be naive to think they won't exist. Sometimes you just have to know whether you are playing by THE rules (and which rules) or the "around here" rules.
Other sports deal with this too. Take golf, for example. There are THE rules (you must putt out, a lost ball is replayed from the previous spot not from where you think it went), but most friendly groups will modify those rules to play the game more quickly and in a more friendly manner. But when it's tournament time, they better know and be able to apply the rules. For most amateur golfers who are teeing it up for the first time in a tournament, this is very hard and typically leads to higher than expected scores (if your buddies give you ten 3-footers per round and you now have to make them, you'll miss some and it is far more stressful).
As someone who is returning to cue sports and is trying to catch up on rules changes, I am surprised by the lack of consistency, as I see things like "break from the box" and "qualifying breaks" and "spotting the nine, not the one ball" and "winner breaks, or alternate breaks" and some tournaments that are doing none of those things and I am left thinking that cue sports can be all over the place sometimes.