I think your expectations are a little high. Friends and neighbors do not "owe" each other anything.
If I understand correctly, they are hosting the party which means they have things to put together, set up , etc for the party. When I was hosting a party, I was pretty busy getting everything done that needed done before the party and assuming that the people who RSVP'd yes would make arrangements to get to the party, not rely on me for that as well.
I understand that it is sometimes a nice thing to offer someone a ride. I was always very picky about who my child was riding with and I never had any issues with getting her to and from myself. I prefer that independence and being in my car.
As for them saying no to you.... don't assume because they showed up with no extra kiddos that they were going straight home after the party. Families have lives, routines and schedules they work around and you don't know what they had planned afterwards. You just took it as in insult that they said no.
I don't understand why this bothers you so much. They were not doing anything offensive... they don't owe you anything, (ride, explanation, etc).