Pierre Hugues Herbert made the same decision. (I would make the point that the Frenchman had rather more to lose than Sandgren, being a top doubles player with a decent shot at a title, or deep run, anyway.)
@Kieran has said many times that he'd have respected Novak more if he'd taken the same decision, as in, just stand by his principles on the matter. Instead, he chose to roll the dice, likely counting on his status to get him through, since he surely knew that his recent covid was not a legal reason for exemption.
With this renewed discussion, it made me think about that Polish woman who was in, and then sent off, for the same reason. Clearly, she got in under the radar. The Polish Federation offered to pay for her legal defense, and instead, she chose to leave without protest. Which surprised me a bit, at the time, since someone else offered to pay for the lawyers. Now, I wonder if she was informed that if she lost her case she could face a ban. Something that maybe she felt she wouldn't have the legal means to fight. Novak, with basically bottomless funds for top-lawyers wouldn't have felt the same distress. Because, even now, he can afford to contest the ban.