The OP is describing dipping, which is very short flossing that also results in a lot of snagged fish. It is common during high water, but also all the time in fast water areas like Tamahi rapids.
I think there are two classes of snaggers:
1. People that don't know any better. They learned from a snagger who told them that there is no other way to catch fish.
Unfortunately the act of flossing causes the bite to go off so only the flossers end up catching fish.
2. People that know better but don't care. Some meat fishers, lazy folks, guides who are under pressure to get their clients into fish.
Gotta agree with typhoon, some people just don't know what the heck they are doing, and were probably shown by someone that "this is how you catch salmon." I remember 8ish years ago when I move to Chiliwack I had never river fished. Some guys from work took me out salmon "fishing" in the Tamahai area. At the time I didn't know it, but we were dipping, in other words, snagging fish in the mouth. We released all fish not hooked in the mouth, and I thought it was an alright way to fish as long as the hook ended up in the fish's mouth.
Fortunately, after fishing with these bozos a few times I started reading some books, reading stuff on this site, steelhead fishing, and learning from my own trial and error. I now look back on those days and shake my head. I feel like an idiot, but I was new to river fishing and it's all I knew at the time.
I have not been back to a "dip hole" in about 6 years. I have zero desire to ever fish that way again. I'd rather go without fish or if I really wanted some, buy it from the store.
The odd time in the lower Vedder where I typically fish I'll end up fishing near someone doing the old cast, drift, R-I-P, reel in. Usually they're catching nothing, frustrated, while others near them are doing well with their short float set up. My usual practice is to walk over to them and politely ask them if they'd like some help with their set up. Most ppl say, yeah sure, I wanna catch some fish! After some gear mods and a quick explanation of how to fish some ppl are generally appreciative. And if they keep doing the damn RIP at the end of their cast I'll tell them that is completely unnecessary fishing this way, and is more likely to just scare the fish off.
I have encountered the odd person who did not take well to the unsolicited advice and told me to F off and mind my own business. No problem. Usually after they snag up for the 10th time, loose all their gear and catch no fish they pack up and leave.
As for the people who know how to fish properly but go snagging/dipping just to bring some fish home and post some pics on facebook? Shame on you. Especially if you are teaching your friends/kids that this is the proper way to float fish for salmon.