I agree with the theory/explanation that your, the psychic's, or your POI's spirit guides may actually block the entire reading or a part of it because you are not supposed to know some details, at least for the time of the reading. I don't have any direct communication with my spirit guides but I felt them numerous times trying to stop me from getting another reading about my ex and my love life when I asked for guidance. The reader I was supposed to read suddenly took a hiatus, stopped responding, refund my money after several days, or they would tell me some details regarding the past and present that I could verify but the future was way way off.
So yes, I believe some spirit guides will only let the reader see a glimpse of what is going on which is why they can say accurate stuff about the past or present but not the future. Also, I have found that apart from trickster spirits who lie intentionally through the reader's mouth, there are spirit guides who are actually deceased humans or spirits of other dimensions who have their own code of ethics and opinions and are not highly evolved or experienced enough to read someone's future--spirits, like us, they can only can make assumptions of what is going to happen based on the past and present energies. For instance, they see that your uncle Mike took the phone to contact you and is about to contact you but his phone suddenly crashes and you don't finally get a phone call, even though the psychic told you he will.
Psychics and their spirit guides most of the time make educated guesses based on the stuff that has already happened and the stuff that is happening in the present. I don't think that they all do it intentionally to harm their clients--psychics can't really filter all the info that comes from spirit.
Another reason why spirit guides may block your reading is that they either don't like your energy or don't like your POI and don't want you to bother with them. If they feel this person is dangerous to your physical or emotional well-being, they will give little to zero info to the reader/channeler that does the reading for your behalf. That is the case with deceased relatives, angels and beings of light for good or for worse. If your deceased granny, for instance, had always warned on you about bad men and preached that you should be careful and stuff, there is a great chance she saw up in the ethers that this guy named Steve is bad for you indeed and tried to manipulate or block the channelled reading so you don't get more info about this person. Spirit guides and deceased loved ones cannot force us to do some stuff like living family and friends, but they can find indirect ways like this to express their approval or disapproval of our life decisions. Perhaps finding a psychic who talks or channels spirits of neutral and dual nature e.g goddesses or high ranking demons with the ability to foretell the future with no bias, would be a solution to this. I don't have much experience but I tried a guy on Bonanza a few years ago, who claims to contact an ancient demon asking about my ex and while it's wasn't 100% accurate, it was far more straight, precise and straight-shooting than the so-called "angelic" new-agey light crap or semi-accuracies I was given from readers who claim to contact angels or deceased relatives.
I've personally lost count of readers who claimed to read with spirit guides who would pick up crazy stuff about my past and present e.g family secrets, habits of deceased family members, but when it came to the future predictions accuracy was next to zero and I was really disappointed. I guess spirit guides involved could not share more info for good or for bad...we can't avoid it, unfortunately.