It's because One is IIS (Windows) and the other is Kestrel (Windows).

• For IIS on App Service, it enables Gzip compression by default, please refer to https://stackoverflow.com/a/34011032/10350621
• For the Kestrel server, you need to use the Response Compression Middleware. Refer to https://learn.microsoft.com/en-us/aspnet/core/performance/response-compression?view=aspnetcore-9.0#when-to-use-response-compression-middleware