Honor does have an effect on interactions with lords in classic, but it won't cause a portion of the faction to instantly like you as it does in Warband. Even if you have high honor, high renown, high relationship with the faction, and high relationship with the lords in your campaign, your allies will still act like children with short attention spans. I'm not clear if you're experiencing mass desertions or just lords running off "temporarily" (for apparently long periods of time) after any hostile that enters their aggro radius. Lords who don't like you or who are currently patrolling/raiding tend not to respond to the announcement of a campaign. Even lords who do respond will have a tendency to run off for periods of time. If you're starting a new campaign far from their fiefs, it may take several days for them to reach you, they don't just instantly appear.
My experience is that it's worse in areas frequented by non-faction hostiles (bandits, etc.) and during sieges in which enemy armies keep hovering nearby actively trying to pull you away from the castle or town. There's nothing you can do, they are just going to run off, either until they've destroyed the hostile or are destroyed by it, or until they lose their target at night. They live to fight, and your summons is a secondary consideration. As long as they are not defeated or captured, they will eventually return if you are still nearby. It does make sieges a little annoying (especially if building a siege tower is involved), and I'm sure we're all agreed that the whole process of sieges leaves a lot to be desired. Total command of your allies outside of a battle instance is just not part of the game, and discipline wasn't something possessed in spades by medieval armies IRL.
Even if you can get your allies to follow you to a siege, there's a chance that any lords who don't like you will sit nearby and not join you when you assault the target. Some of them are just d**ks like that (Lord Bulba, I'm looking at you).
My advice is to cultivate friendships with a handful of lords who tend to have large armies, recruit only them and in person, don't lead them into a fight with an enemy who has a substantial numerical advantage, and don't sit back and let them to all the work (that is, don't let them take all the losses if you can help it). They'll follow you anywhere (they'll still run off periodically after anything that aggroes them), and they'll vote repeatedly for you when the marshall election comes up.
Annoying? Very. But some things just can't be done alone.
