There should be an incentive to encourage hosts to interact with guests to try to get the party to level 10.
If I join a friend's party and see that they have started their party and logged out shortly after and then their party does not hit level 10, I remove them from my friend's list.
Even if your lot does not have the room to have a lot of party activities, hobby activities and job activities, as a party host, you are able to interact with party goers without needing energy.
You get 25 party points per friendly or flirty interaction so even if you have only a couple guests, as a host you can interact with guests to ensure that your party reaches level 10.
If there was incentive to reach level 10, perhaps fewer people would start a party and log out.