First, it's worth making clear that no prediction about anyone else or yourself (even if you do it for yourself) is set in stone because, at any moment, we have the potential to completely change the thoughts we dominantly think. See When fortune-telling or predictions come true, do the results come about because of the Law of Attraction?

But, aside from that, and to answer your question, it's the same reason that the solution to other people's problems are usually easy to see, whereas the solution to your own problems are usually difficult to see.

You have a greater level of "detachment" from the issue when you are dealing with others, instead of dealing with yourself.

You see this happen on IQ regularly. It's usually obvious to others where someone else is vibrating but they just cannot seem to see it themselves because they are so immersed in their own issues.

The same thing happens for "vibrational readers" too. In that category, I would put psychics, clairvoyants, channellers, and anyone else that picks up intuitive information.

Even vastly-experienced channellers, for example, say they find it much, much easier to provide channellings for others than for themselves.

That's the high-level explanation but you seem to like details :) ...so here is the more technical explanation...

Basically, you cannot "Ask" and "Allow" at the exact same time

(Step 1 & Step 3 are different)

They are different vibrational states. One is the vibration of the "problem" and one is the vibration of the "solution" and you have to be in one or the other at any particular time, otherwise you would not be able to differentiate a problem from a solution. See How do I channel experience of meditation to art?

Some highly-gifted vibrational readers are able to switch quickly from one state to the other but even they cannot achieve both states simultaneously...at least from a 3D physical perspective.

I used to be good friends with a guy who was highly-gifted psychically. When he had to provide information to others, he would be flooded with impressions that would easily flow off his tongue. But when it came to himself, he would be stuck.

I remember him coming around on occasion and me having to sit there asking him questions about himself that he had given to me to ask a few minutes earlier. It was because it was much easier for him to "receive" if someone else was asking his own questions :)

But even if you are able to "receive" information for yourself using tricks like this, you still have to interpret the information you have received. And if you are too wrapped up in your own issues, you can still find it hard to be detached enough from them to clearly understand the information you are being told.

And, even after that, even if you accurately interpret the information, you still need to apply it in your own life...which is a lot easier said than done, whether you are a "vibrational reader" or not.