Huh? People are thankful for what they have, even if they aren't sure how they got so lucky. I'm thankful I wasn't born during the black plague. Should I thank God for that? Then the people who died of it should curse God for it. You can't have it both ways.
Why is this not computing in your brain? No one said people can't be thankful. No one said people can't be thankful FOR things. That has nothing to do with what was said, so why do you continue to think that's the argument?
When you display gratitude (i.e.; give thanks) you have to express gratitude TO an object because it's an adverb. It makes no rational sense otherwise. Who are you thanking? Imagine if you were watching the music awards show and Jazzy Z won and stepped up to the mic and said... I would like to thank! IF that was all he said, you'd think he's on drugs or something because it makes no sense until something else follows.
So whenever you say that you are "thankful" there has to be an object to apply that adverb to. Whatever you are thankful FOR is not the object of your thanks because that doesn't make any rational sense. If Jazzy Z says "I am thankful to this award for being an award I am thankful for..." again, you'd think he must be on drugs.
Are you on drugs?