(And going back to the other Pokemon Center not having a problem... Stone Town is small and would likely be a bit more lax. Fuchsia City is a large metropolitan area with a lot of tourist traffic. The center would need to be quite large to accommodate a sizable population of trainers, plus the visitors who would be coming by for the Safari Zone/Pal Park. It would be reasonable that they would have different rules, particularly if one of their biggest draws is the Safari Zone/Pal Park. Large gatherings of trainers during peak seasons would present a problem if they all have walking Pokemon, as space would quickly become an issue. Also, during peak seasons, the possibility for crime would escalate and we know that stealing Pokemon is a very common occurrence, and with the Safari Zone/Pal Park importing their Pokemon, the rate of theft would be relatively high.)