On the flip side they are also NOT seeing these problems with the vehicles on the shorter oil change intervals, but they are seeing them fail on the higher change intervals. Then they give their advice. Because they are the ones seeing it on a daily basis...seeing why it happens, seeing others not experiencing it...seeing the trends and correlations, will always lead a tech to say, "don't do that". It's the way it is.
It's like a stock broker telling you not to buy in a certain sector because he's seen people lose there (yet plenty do well in that sector). Or a doctor telling you not to eat high cholesterol/saturated fat foods because they can lead to heart attacks - because that's what he sees and that's the industry trend - yet others won't have heart attacks, many actually, or they'll be a new study saying cholesterol won't give you a heart attack (and five years later that's proven wrong). People in industry give advice off what they see, what they experience, what the trends are, what is happening now enough times to say...ok, there is something here with THIS. Same for guys who install widows, vinyl siding, hot water tanks, cook, clean, bake, paint, cut hair, grow plants, cut grass, sell watches, insurance. They're going to tell you what is best, a lot of times we won't take their advice and a lot of times it doesn't matter because we won't keep whatever it is long enough or use it to the extremes they consider "normal". And yet there are times we should have taken their advice (I've learned that too). Lol.