We are in the first year of a brand new console generation and as a result, last-gen consoles have a limited amount of time left in production. Over in Japan, Sony is getting a jump on cutting back the number of PS4s it produces, discontinuing a few different models.
Sony Japan has discontinued all models of the PS4 Pro in Japan and the original PS4 (CUH-1000) design. The 500GB PS4 Slim (CUH-2000) is still in production though and will be the only one left in Japan for the foreseeable future.
This frees up resources for Sony to use that manufacturing space on PS5 consoles instead. Up to this point, PS5 consoles have been extremely difficult to come by as consumers battle with scalpers for limited retail stock. Sony can combat this problem by producing more. Less PS4s being made ensures more PS5s can be produced instead.
Sony has not commented publicly on the discontinuation and we do not yet know when PS4 models will be discontinued in other regions, but we can expect to hear more on that in the months to come.
KitGuru Says: Given the demand situation, it makes sense to begin phasing out PS4s and replacing them with PS5 consoles a little earlier than planned. Hopefully by the second half of this year, the next-gen console stock situation will be much improved for both Sony and Microsoft.