Not because of any high falutin' reason, but simply because Trump always wants everything to be about Trump. This is how he wins. Impeachment is of course about Trump, but he will attempt to saturate the airwaves with his personal battle and drown out all else.

Theoretically it's possible, but there is little room for error, and with the Senate still unlikely to convict, not much upside.

What happened with Nixon is not helpful. Nixon and his Republicans had limits. Today, Trump and his lackeys have no limits. Far more dangerous than Nixon, and zero chance he would resign to spare the nation a battle, as Nixon did.