Because God disappoints.
Are you excited yet? There's more.
His priorities are better than yours and your happiness isn't at the top of the list.
WHAT?????? BUT I DESERVE TO BE HAPPY!!!!!!!
Relax. He has something better in mind when He delays your happiness.
And don't hate me, but I don't even mean that He will spare you temporary happiness in order to give you lots of happiness later. That's true at times, but He's still better than that.
WHAT???!?!??? JOSHUA, YOU GO TOO FAR!!!!!!
Here's a picture of a kitten to distract you.
See, He's all about His glory. Sometimes it's congruent with your agenda and sometimes it isn't. That's hard to swallow, I know, but God's agenda needs to come first for everyone's sake. His way, His Kingdom, His ideas are more important than you and what you think you deserve. It's not rude, it just is. It seems harsh, but let's pan this out a bit.
To be mad about what I just said, is to say this: "More important than God's glory is _____".
If you're like me you might say "well, can't God be glorified while I'm happy?" Yes! Of course. It's just that the happiness flow is bound to get interrupted and we shouldn't be surprised when it does. It's part of the Christian journey.
Just chew on that for a while. Be angry if you need to be. Then maybe keep reading if you can.
Now that we got all that out of the way, let's talk about how much Jesus cares about you and wants good for you (we need this detour before I can really drive the point home). God has more life in store for you than you can fathom. The promise is more life than we can imagine or contain. That's straight up Bible right there. Paul told us we can't even understand how much Jesus loves us. We get joy and peace in Jesus, by the Holy Spirit, high-fiving the Father (okay, I made the last one up). The Christianity thing may not always be comfortable, but it is good. God is generous, kind, merciful. It's called "the good news" for a reason.
Now that you know where I stand on all that, let me point out that I see a disease in my fellow humans. Those under thirty seem to have it worst. It turns us into crazy zombies, and instead of crying for brains we say:
I'm entitled to happiness.
We want a lot. We want it quickly. We want it to be cheap.
Where did this thinking come from? Perhaps it's Amazon Prime (which is sweet right?), Netflix (which I use everyday), or growing up with microwaves. Whatever it is, it's not helpful to our souls. We could use our parents' work ethic, and we could use a reminder that we don't deserve perpetual happiness (ouch. I know it's tough).
The ironic thing is, for people who stomp their foot and say "nay cruel world! I need happiness!" happiness tends to elude them. Those who are savvy life-hackers know how to embrace difficulty, sadness, and disappointment as beautiful. They don't avoid those things. They let go of the demand to have life a certain way and their highs tend to be higher as a result.
It's shockingly similar to this thing a buddy of mine said about "finding your life by losing it."
Sometimes a Christian is disappointed. Not all the time. Happiness isn't illegal. But even our role model, Jesus, was pretty bummed out about the whole cross thing. He asked God to take it. God didn't. Jesus dealt with it and still managed to go the cross with joy.
So, you Christian (especially you young Christian), say it with me!
I am not entitled to happiness. God is more interested if gifting me with a full life, which is painful sometimes. More important than any of that is His glory and knowing Jesus more. It's better for everyone that way.