Even in that case accepting the pardon is considered an admission of guilt. That’s something that’s been repeatedly underlined by the courts in the years since, including very recently.
Beyond that the Nixon pardon was and is legally dodgy. It was pretty carefully never challenged, because it probably wasn’t kosher. Both pre-emptive and blanket in nature nothing could be enumerated or acknowledged since there were no charges yet and the bounds of the pardon were “everything surrounding Watergate”.
But I’m not talking legal technicalities here. Look at Trump. Is that a guy who is ever going to acknowledge that he needs a pardon?
The guy was fixated on the idea that he’d be impeached from the minute he stepped into office. Grousing that being impeached would ruin his legacy and the glory of his presidency. And it still didn’t stop him from repeatedly doing impeachable things. And until he went dark he was still obsessively painting it as illegitimate.
I just don’t think the guy could stand the idea that anything he’s done is wrong enough to require pardon, or the idea that being the a pardoned president is his legacy.
He can’t conceive that consequences exist, and his only concern with these thing is how they look.