Why does weakness seem to be so valued in the kingdom of God? Is God cruel? Does He want us to be weak? Does God delight in seeing us struggle, and suffer, and squirm?

Not at all. When we understand by divine revelation our poverty of spirit – that we can do nothing of eternal value on our own, that we cannot save or fix ourselves, that without Jesus we are destined for wrath and eternal punishment and torment for our sin – we are driven by necessity into His loving arms, into His grace, into His mercy, and into His strength. Without the gift of weakness and suffering we remain dependent upon ourselves instead of depending upon Him.
This is the very reason God allows us to get into situations that are over our heads, where we feel like we are drowning. It’s a test. Will you lean into Him or will you run? Will you receive His strength or go it on your own? Will you receive His grace or depend upon what you can do for yourself to try and wriggle your way out of it? Will you try to fix it or simply trust in His power and ability to do that which you could never do?
It’s at the times when I feel the weakest and I lean in and simply receive His grace that my weakness turns into strength. “By His divine power, God has given us everything we need for living a godly life” (2 Peter 1:3 NLT). I just receive it. I don’t have to work for it. He gives it by grace, not because I’ve done anything to deserve it.
In fact, the weaker you feel, the greater the opportunity to be strengthened by the Lord. Therefore, the apostle Paul could say,
But the Lord said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” Therefore I will boast all the more gladly of my weaknesses, so that the power of Christ may rest upon me. For the sake of Christ, then, I am content with weaknesses, insults, hardships, persecutions, and calamities. For when I am weak, then I am strong.” (1 Cor. 12:9-10 ESV)
This is also why Jesus told us, “Blessed are the poor in Spirit for theirs is the kingdom of heaven” (Matt. 5:3 ESV). Those understand their great need for Him, and who understand they are helpless without Him, receive His kingdom. Remember, we are sons and daughters. We are co-heirs with Christ. “It is your Father’s good pleasure to give you the kingdom” (Luke 12:32 ESV).
That is the mystery of the kingdom; the revelation which must be revealed rather than learned. “When I am weak, then I am strong.”