https://blogs.fangraphs.com/april-attendance-matters-for-mlb/
Attendance in April isn’t likely to make or break a team’s season at the box office. Numbers generally trends upwards from the beginning to the end of a season. Nor is that surprising: the weather gets better, kids get out of school, and the games generally have greater playoff implications.
April’s attendance numbers are more often based on a combination of expectations and tradition. Teams that are expected to be competitive — the Cardinals, the Dodgers, the Giants — are going to sell a lot of tickets. As the season progresses, of course, clubs that fall out of a playoff race can expect a decline in attendance relative to their more competitive seasons. Conversely, teams that have surprisingly good years can see increases.