The reasons why the number of successful students in each class of the primary school lottery are almost the same are as follows:

1. Lottery rule setting: The lottery rule sets the enrollment limit for each class. Make sure the number of students in each class is relatively balanced. This can prevent certain classes from being too large or too small and ensure the rational use of teaching resources.

2. The lottery method is fair: The lottery method is conducted by random drawing to ensure fairness and impartiality. Each family has an equal chance of winning a spot, resulting in a relatively even lottery for each class.

3. School resource allocation: In order to ensure the teaching quality and the appropriate number of students in each class, the school will reasonably arrange the number of students enrolled in each class based on the allocation of teaching resources.