Large churches from other denominations, like Catholicism, are not included as they are not deemed to belong to the megachurch phenomenon which by definition is part of Protestantism.
The list is not exhaustive, there are large annual changes, and there are difficulties to compare the churches as different methods to count can be used.
There is an obvious psychological boost from reporting growing numbers, "success", for enhanced credibility and motivation to support the work.
The megachurches are often formed around a strong leader that stays in charge for decades, it is often like his "own personal enterprise", many times with limited economic transparency, a tendency that has been questioned in various countries.
Thus, in cases of irregularities, a pastor may continue without disciplinary measures, due to their sheer power, and any disappointed members may leave but new people keep coming in, with reduced effect on attendance.