#1. To reaffirm Randy Orton as a sadistic villain

This is the Randy Orton that we truly missed seeing. When he was still a young rising prospect, he made his name as "The Legend Killer" - a sadistic heel who would go after anyone and everyone.
Women certainly weren't off-limits to his assaults either and Beth Phoenix isn't the first woman to experience the RKO. Orton admitted a few years ago that he's far more comfortable being a heel and he said this while being an established babyface on SmackDown.
He turned heel in 2018 but the run didn't quite have the same effect and results as one might have hoped. It took Edge to return to end his short-lived babyface run on RAW. And perhaps his return after 9 years motivated Orton, who normally isn't known to put in a 100% (not in the past decade, anyway) seems to be giving it his all in this rivalry.
RKO'ing Beth Phoenix reaffirmed him as the sadistic villain of old - which is exactly what he needed at this time.