Just talking out my butt here, but I think on most votes they have a pretty good idea of where most congresspeople plan to vote and whether or not the amendment will pass. So if some republicans knew it wouldn't pass with their yea vote, they could have felt comfortable giving it a yea as taking credit for standing up to "the administration." Whereas they may not have actually given that vote if they thought it mattered. This opinion is based on no other data than watching House of Cards on netflix and Veep on HBO.