There are different schools of thought. Some people think the teachers put effort to serve and hence they should be given the best priority like Phase 1, while some think like you that they shouldn't have any priority. Again you can't please everybody. 2A2 I guess it's the best middle ground for them.
For teachers it's more of logistics reason for them to place the children in the same school - they already need to report work early, if they need to send the children to another school before they go to work, would be super earlier for the children.
Of course there will be some teachers who try to get a position in a school of their choice in order to gain priority entry, but honestly if these schools are popular, as much as you want to choose the school, the schools are also picky in their choices. More than often these teachers don't get a place in their preferred schools