TL;DR: Weiss had already been confirmed by the Senate. Smith wasn’t. That’s the difference.
U.S. District Court Judge Mark Scarsi memorably wrote:
“The misstatements in the current motion are not trivial. Mr. Weiss’s institution of charges against Mr. Biden in his capacity as U.S. Attorney offers a meaningful distinction between this case and the nonbinding district court decision on which Mr.Biden bases his motion.
But Mr. Biden’s motion does not engage with this distinction; instead, counsel avoids the issue by misrepresenting the history of the proceedings. This Court has little tolerance for lack of candor from counsel.”