Why no flavor_USES helper?

From: Mel Pilgrim <list_freebsd_at_bluerosetech.com>
Date: Sun, 05 Sep 2021 17:39:29 UTC
The flavors helpers like flavor_RUN_DEPENDS are super useful, but I need 
to modify USES based on flavor, and find that there is no helper for it. 
  That is, I'd like to be able to do this:

flavor1_USES=	alice
flavor2_USES=	bob

Instead of:

.if ${FLAVOR} == flavor1
USES+=	alice
.elif ${FLAVOR} == flavor2
USES+=	bob

At a glance, it looks like all that's needed is adding USES to 
_FLAVOR_HELPERS_APPEND[1]. What am I missing?

1: Mk/bsd.port.mk, line 1525 as of bed4073e0