Why do some people only believe it, and not experience it? Why are their interactions with his goodness so few and far between?
God shines his light in your life to the extent that you allow him to. Most people do not allow him to.
How do we block ourselves?
We are closed to correction.
Enough cannot be said on this topic. So few people use this tool to the extent they could.
We can't just meander through our best idea of what life should be and expect to encounter the full measure of God's intended blessings. We are fallen creatures, and we are far from God in wisdom, desires, and knowledge. If we do not seek correction from every source available to us, we are in some ways cutting ourselves off from a measure of greater blessings in our lives.
We don't introspectively connect our pain to opportunities for self improvement.
Every time you experience pain or disappointment, do you feel sorry for yourself, or do you see it as an invitation to improve your understanding of yourself and the world? Do you ask yourself "why didn't my desired outcome occur here?" Do you consider what you could do to make it better in the future, or do you blame things and people outside of your control? Do you conform your expectations to more accurate revelations of reality, or do you insist on maintaining your ideologies even after they have been proven wrong? [Sidenote: This is a massive problem in modern society, and in my opinion will be the reason for its collapse. We want things to be how we want them to be, without regard to the constraints of reality. Simply put, we love our lies.]
Some pain is necessary and unavoidable in this life, but the vast majority of what we experience is not necessary or even useful. Mistakes are necessary for learning, but if you are perceptive, you can let other people do the mistaking. You can learn from others' mistakes. If you are not perceptive, you have to learn from your own mistakes. If you are humble (that is, teachable), you will never make the same mistake twice.
We are too busy.
The Lord said: "Seek not to be cumbered." (D&C 66:10) Are you encumbered?
Do you have every moment of your day scheduled out? Do you put first things first? Do you have a dedicated window of time for God each day? I give God the first chunk of my day, every day. It has made all the difference in my life. I wake up a few hours before everyone else in my house, and I spend the time working on my mind, body, and spirit. I refuse to think about anything temporal, except the rare case where that is what God directs me to do. Every single day I learn more about him, no matter what else happens during the day.
I've structured my life so that throughout the day, any time I get an impression from God I can, not much time later, take the time to follow it to its end. I take notes. I look things up. I think. I pray.
Some of these changes can be made instantly, some take time and deliberation. You can immediately start waking up (and going to bed) earlier. You can immediately reduce activities you do through the day that do not mean much. You can immediately work on focusing more at work to free up the part of your work day you spend on Facebook or otherwise wasting time. You can limit the number of extracurricular activities you drive your kids to. Etc.
We are too closed minded.
We can be closed minded in big ways, such as turning away from what we know God wants, but I think the more subtle tragedy is when we miss the small things that end up being big things. These things are almost imperceptible.
The blessings of eternity turn on surprisingly small hinges:
6 Now ye may suppose that this is foolishness in me; but behold I say unto you, that by small and simple things are great things brought to pass; and small means in many instances doth confound the wise.
7 And the Lord God doth work by means to bring about his great and eternal purposes; and by very small means the Lord doth confound the wise and bringeth about the salvation of many souls. (Alma 37)
I have watched as people pray for blessings that are righteous requests. God then sends a small test or a small decision to them to take them to where they have requested to go. Then, flatly, the person fails the test or refuses to make the right decision, and they accuse God of not listening to their prayer, and question their faith.
When the Spirit is upon me and I look back at my life, I am absolutely amazed at the plentitude of experiences where massive outcomes followed from small imperceptible decisions. By exercising a wide open mind, I consider actions that seem unusual or extreme. I am open to pretty much anything. Sometimes this leads to false positives, experiences that would have been better not to have, but most of the time the experiences make all the difference, and even when they are not expedient, it becomes very obvious very early, and not much harm is done.
We want immediate, obvious, easy results. God sometimes works like that, but those who limit his gifts to those will be leaving so much more on the table.