Monsters and Syndicate can go for a loyalty mechanism. I really like the idea but in fact, If you go for it you can't use any lock cards as there is no card in both factions with this ability. It makes them highly vulnerable for all "all in" strategies (ex. Kolgrim). I don't know if this is done "by design" but it would be nice to have at least one card with this ability to allow more flexible deck builds.
I assume you mean devotion when addressing loyalty, and I understand your point. I believe the devs' understanding is that you need to limit your card availability in order to activate a faction's devotion advantages. This trade-off really can highlight a faction's weakness, such as lock availability for MO and offensive purifiers for NR. Well, apart from SY that is, probably that's the one faction without inherent deficiencies - even if doesn't have a faction lock.