The rationale is that I've found wanting to play as 'security' or as bodyguards is one of the more common immediate goals for new players, and these coded types of jobs are both not numerous and mostly intended for experienced PCs.
And while you do see new characters often attempting to play as freelance security of various kinds, there's not often a lot of actual purpose for this role: Immy on immy violence does happen, but the threats a new immigrant often will face are not anything that can be deferred by an immy combatant-for-hire.
Having some relatively weak ambient threats around that are a danger to non-combat characters but can be managed by relatively inexperienced combat characters, might encourage more 'bodyguard for hire' type roles. Give a reason for someone to ask an immy combatant to escort them over to the shops or whatever.
To make sure they're not wiping people out and discouraging characters going outside, they could only be hostile occasionally and also not inflict bleeding injuries, and maybe no cutting that would damage clothing.
Could even have the rare ambient terrorist or vee-addled mixer on Gold to encourage running errands with someone from your Corporation's security team.