You're not the first to think this, and obviously not the last.
Fasa had brought up the idea of Neo-Feudalism in the earlier source books, and it does seem to make FASA-nomics makes sense. But, it does more than that. Or it should do more than that. A lot of emphasis has been placed on mercenaries as the go-to force for players to dabble in the factional waters a bit, and have a unit that can potentially see a lot of combat.
Where do a lot of those Mercs come from? How many of them are old retainer forces from a deposed minor noble an a certain planet? Dispossession is a negative status mark. But, that's on a simple social level among nobles. A lord/lady dispossessed for whatever reason may be loved by his/her vassals. If that happens, they might not simply change flags and take orders from the next noble to be given the castle. They might up and go ronin, following their beloved leige on to new adventures regardless of what it may look like.
How many are spare retainer forces belonging to a minor noble that get hired out for a little side hustle?
How often do you really have to bring someone from off-world when a lot of planets should have their own glut of small-time swords-for-hire? And how many nobles might be looking to hire on any given planet at any given time?
How often would a mysterious band of pirates that sprung up out of nowhere turn out to be retainer forces for a noble sent out in disguise to ruin some pet project of a rival lord or lass? Nobody might actually guess unless it's scrutinized even loosely.
Finally, an honor code and right of refusal might explain why some raids could land unmolested on many worlds that aught to be highly defended. IF almost every viable target is under the pervue of a noble, and it's a matter of honor for that noble to handle the defense on their own, they might get a call for the central hub and be given the option to do so. There is always the option to say 'you handle it', but doing so could be a mark against the noble's status.
Heck, there might even be an honor system loosely matching the Clans's batchal. Mercenaris could be using a raid to make a name for themselves and/or their employer. They can actively announce who they are, and name their target. This, too, can allow them safe passage to their mission site, and it's up to the Noble owning the target to decide whether the local defense will need some back-up, maybe losing face if they decide the target is just too valuable for honor. Or, honor may be more important that the target, and they can risk the potential loss if the noble's forces are outsmarted, out-maneuvered, or out-performed.
Such challenges would distinguish a sponsored mercenary raid from that of a pirate force, who may announce who they are only after the raid is finished if they're trying to make a reputation.
I understand why they decided to focus on mercs as where all the action is. Let's face it, Front line forces will only see action when the head government gives them a call to action. But, a lot can be done by using nobility and feudalism on top of that so that you don't have to go off-world for the next mission. And, if a standard BattleTech is any semblance of Mech combat in the BTu, any form of combat will chew through machines all too easily. Some of the manufacturing numbers suggest there are loads of chassis available for use and piles of spare parts to fill in a lot of gaps all to make up for that potential rate of turn-over.
