Since you asked...
1) It's not a choice of a 9/10 or 10/10 school. Lake Forest Elementary, the school SVUSD assigned The Meadows to, is a 5/10 per GreatSchools.org
2) Lake Forest Elementary is roughly a 15 minute drive from The Meadows. Potentially 4 times per weekday depending on the family's situation. There are more many productive uses of time than driving an hour per day for school pickup/drop-off.
3) I agree class size isn't the single determining factor in education, but it does make a difference, especially when kids are young. 30 children in a classroom with one teacher can quickly turn to chaos and interfere with learning. It can be miserable for the teacher as well, which can deter desirable teachers. It's also indicative of how the school/district is managing it's resources and how much resources they have. Larger class size suggest they're short on resources or allocating them poorly.
4) Parents generally want to give their kids the best start possible. The best schools, the most quality time together, and so on.
A new school in the neighborhood is a step towards #4 and is attractive to families who place a high value on devoting resources to help their children excel. Irvine Company / City of Irvine recognizes this. The builders at Tustin Legacy / City of Tustin recognized this. Even TB recognizes this, which is probably why they pulled this marketing stunt. But these are apparently not priorities to SVUSD or Lake Forest