Why does God want to keep us...

[Strong in Him]

Why does God want to keep us weak and dependent and pathetic all the time? It's so boring...

Who says that he does?
"Weak" - in what way? We are told to be strong in the Lord and in his power, Ephesians 6:10, because our struggle is against the evil one. Peter tells us to resist the devil, 1 Peter 5:9, and be strong in the faith. We are told to put off our old selves, Ephesians 4:22, to put aside envy, Jealousy, anger etc etc.
We are told to pray at all times, to pray for others, to give thanks in all circumstances.
Look at all the suffering that Paul endured; beatings, opposition, stoning, pressure from his churches.
You don't think that, maybe, this requires/required some strength?
"Dependent" - upon God? Yes, of course. He made us, saves us, fills us with his Spirit and is the author and perfector of our faith. We cannot save ourselves, that is the Gospel. If we could, we wouldn't need Jesus.
We depend on God to give us all things - but we still have the right to be the person that he made us to be and to use the gifts that he has given us. If we know we are called to a specific task/ministry and someone else tries to divert us or take us away from that, we have the right to say 'no'.
"pathetic" - where are we told that God's children are, or need to be, pathetic?

 

[Strong in Him]

I don't see why and how having some self-sufficiency would be so detrimental to God's purposes

What do you mean by "self sufficiency"?
We have the right to use the brain that God gave us. In fact, as we are instructed to love God with our minds, we should do so.
We have the ability to choose and make decisions.

We even have the ability to reject God completely, try to save ourselves and claim that we will live our own lives and do it our way. Some do, and outwardly they seem to do fine. It's the age-old question of "why do the unrighteous prosper?"
But ultimately, it will fail.
If we do not turn to God, trust him and depend upon him now, we might find that, after death, we WANT to depend on him to save us, but it will be too late.