If while shooting raw images "you have great flexibility to adjust the white balance," then why does any adjustment result in images being declined?

I'm advised under the possible reasons for images being declined that, "When you shoot in raw formats, you have great flexibility to adjust the white balance in your post-processing workflows."

If I do so in the least, using either auto/manual adjustment on anything with PS or LR, then they tend to deny my images and advise to leave altering anything up to clients.

If they honestly want clients being able to alter the WB or tint/exposure etc, then why insist on me uploading JPG files instead of DNGs?  Doesn't this JPG format commit absolute changes that can't be undone at a later time, even with stuff as slick as PS tone editing?