The Sony PS5 is expected to be released later this year. Given the popularity of the PlayStation series in general, we expect that there will most likely be a rush of gamers eager to place their orders. In order to ensure that gamers will be able to purchase the console, it seems that Sony could be employing a preventive measure that will limit one console purchase per household.
This is according to a post on Reddit in which it details the backend code for PlayStation Direct where it suggests that only one household may order one PS5 at a time. Presumably this is done to prevent people from purchasing multiple units at once in order to resell them at higher prices due to potential limited supply at the start.