The purpose is gatekeeping, and setting a minimum basis of quality. If the annual fee was $0/year developers would be worse off due to the flood of low-quality

The purpose is gatekeeping, and setting a minimum basis of quality. If the annual fee was $0/year developers would be worse off due to the flood of low-quality applications. This is exactly what happened on Steam when the platform was opened to anything for a $100 submission fee - quality tanked and revenues even for established Indie developer have declined significantly.