I think if Roberts had gone along with Impeachment 2.0, and Trump was impeached, the congress case would have then gone to the SC on grounds of it's constitutionality and Roberts would have had to recuse.
In that sense, Roberts was just reading the writing on the wall and looking out for Roberts. He would have run a trial that could potentially be overturned by the SC that he is the Chief Justice of. Not a good luck going forward. Might be one of the other judges is making a play for that CJ position, and Roberts is on thin ice.
Roberts MO, IMO, is to try to not blow his cover wrt to votes on non-essential or obvious cases. He votes with the conservatives on minor issues so he can fuck them over on major ones with some degree of deniability.