the rule says you have to have good cause and the neglect must be excusable.
The rule does not say that. The rule (and all the cases interpreting it) describes two different standards. One for pre-deadline extensions, and one for post-deadline extensions.
Utah courts tend to routinely agree with your view, but the appellate courts seem to routinely disagree. See Quigley v. Rosenthal, 427 F.3d 1232 (10th Cir. 2005) (untimely motions to be considered under excusable neglect standard), Livingston v. Univ. of Kan. Hosp. Auth., No. 20-3075 (10th Cir. Feb. 11, 2021) ("By the time she requested the extension, her deadline had already expired. So she needed to show excusable neglect."), Lopez v. Cantex Health Care Ctrs. II, No. 23-2044 (10th Cir. Nov. 7, 2023) (motions under Federal Rule of Civil Procedure 6(b)(1)(B) to be considered under excusable neglect standard),
Hamilton v. Water Whole Intern. Corp., 302 F. App'x 789 (10th Cir. 2008) (same),
Rachel v. Troutt, 820 F.3d 390 (10th Cir. 2016) ("Because the motion was timely, he needed only to show good cause for the extension request.),
Babakr v. Fowles, No. 23-3026 (10th Cir. Apr. 5, 2024) ("Under Fed.R.Civ.P. 6(b)(1)(B), a district court has discretion to accept a party's late filing if the party files a motion showing that the delay was the result of "excusable neglect.", "under Rule 6(b), a post-deadline extension . . . is permissible only where the failure to meet the deadline was the result of excusable neglect"
Ignoring linguism, consider this? What point is there to have good cause and excusable neglect for post-deadline motion, when one of them is much stricter than the other? Even if your linguistic view is accurate, that still doesn't change the fact that one of the standards would be a non-factor. If memory serves, courts routinely frown on such interpretations.
To the extent you imply that both standards would also apply to pre-deadline extensions, that is completely and totally incorrect.