SSR is not specific to JS. You can do SSR in old-school PHP. People care about SSR because it relates to how Google ranks your page, among other concerns. SSR

SSR is not specific to JS. You can do SSR in old-school PHP. People care about SSR because it relates to how Google ranks your page, among other concerns. SSR is also part of a larger story of optimization which touches upon network concerns, such as making network requests on the server rather than on the client.