If it wasn't security they'd just pick a different pretext. "Oh you violated some comma in the 1k page eula, we gotta ban you now, can't set a precedent of allowing violations ya know" or some crap like that.

Security, safety, liability, risk, equity, inclusion, god, any word or concept that it is not socially unacceptable to consider anything other than an unalloyed good WILL be used in this way.