There are many issues that can cause no decode. I have had guys tell me over the phone that they can see signals on the waterfall and yet no decode, and it turned out they did not have the proper codec selected and were looking at noises in their own room picked up by a laptops built in microphone. Yet they thought it was FT8 signals. Having never seen an FT8 signal how would they know?
Having looked at many guy's waterfall with desktop sharing software, I am appalled at how poor many fellas antenna systems are and how much locale noise they have to deal with. They might be getting 3 or 4 decodes per pass when they should be getting 50 decodes at least per pass on the weekend on 20 meters.
And what you can "fix" in 2 or 3 minutes in person can take an hour over the phone. Your eyes are someone else's eyes, your hands are someone else's hands, and your brain has to convince another brain to think like you think. Solving problems over a phone is hard. Solving problems over a forum, can be even harder.