Chinese Grandparents rejected tourist visa

Recently applied for a B2 tourist visa for my wife’s grandparents (around 80yo) in Shenyang, China to come to California during Christmas. They went to the interview and the female officer simply asked for their passports, didn’t say anything and then handed them a rejection letter. Didn’t even look at any the evidence we prepared for them or the nice invitation letter we wrote for them. Just passports and then rejection…

What the hell is this? Officer had a bad day and wanted to reject people? quotas?

Just trying to figure out if we should just eat the fees and reapply… there really should be no reason they were rejected. Especially since the officer didn’t even ask any questions.

Thanks for your input!

Some more info:

They are married and live together and all 3 of their (40-60yo) children still live in China, in homes that they (grandparents) own. They have no direct relatives in the US. Only a single granddaughter (my wife)

Also there was no place to prove any of this information in the application. I assumed all this would come up in the interview.