Everything that happens in this world happens at the time God chooses.
– Ecclesiastes 3:1
I don't know why either. But I trust God's timing.
Always pray to God - not to grant you your wishes, but to grant you the wisdom of what He wishes from you. And while you are at it, you might as well thank Him for all that He has already blessed you with.
Lord, may I always remember that Your promises are true & are eventually being fulfilled in me.