In seeking for an explanation we may perhaps trust, at least in part, the evidence of the Ethnicon itself.
The addition of the -ati- suffix to the -no- ethnicon, as in Iguvinates, is comparatively rare, and no doubt denotes the opposite process, namely, the absorption of a -no- tribe by a population to whom it was natural to use the suffix -ti-.
The derivative adjective Aequicus might be taken to range them with the Volsci rather than the Sabini, but it is not clear that this adjective was ever used as a real ethnicon; the name of the tribe is always Aequi, or Aequicoli.
The Samnite and Roman conquerors tended to impose the form of their own Ethnicon, namely the suffix -NO-, upon the tribes they conquered; hence the Marruci became the Marrucini, the *Arici became Aricini, and it seems at least probable that the forms Sidicini, Carecini, and others of this shape are the results of this same process.