gp is probably thinking of system.text.json which was only added to .net core in version 3, which less than a year old. But it's not been high priority to add b

gp is probably thinking of system.text.json which was only added to .net core in version 3, which less than a year old. But it's not been high priority to add because of a very well established open source project called JSON.net that has been around for ages. However the full framework has had a different JSON serialiser (DataContractJsonSerialiser) since v3.5 in 2007.