There are 1000 reasons why, but in short:

.NET 7 got about 1000 performance-impacting PRs across the runtime, core libraries, ASP.NET Core, Windows Forms, Entity Framework and beyond.

Here's a quick summary of what got improved:

𝗝𝗜𝗧 𝗖𝗼𝗺𝗽𝗶𝗹𝗲𝗿: Superior assembly code dumping, inlining, and vectorization.

𝗚𝗮𝗿𝗯𝗮𝗴𝗲 𝗖𝗼𝗹𝗹𝗲𝗰𝘁𝗼𝗿: Enhanced memory management with reduced fragmentation.

𝗡𝗮𝘁𝗶𝘃𝗲 𝗔𝗢𝗧: Improved startup time & reduced memory usage.

𝗠𝗼𝗻𝗼 𝗥𝘂𝗻𝘁𝗶𝗺𝗲: Tailored for WebAssembly & mobile platforms with better code gen.

𝗥𝗲𝗳𝗹𝗲𝗰𝘁𝗶𝗼𝗻 & 𝗜𝗻𝘁𝗲𝗿𝗼𝗽: Faster type loading, dynamic method performance, and new source generator attributes.

𝗧𝗵𝗿𝗲𝗮𝗱𝗶𝗻𝗴: Enhanced thread pool scaling and synchronization.

𝗖𝗼𝗿𝗲 𝗟𝗶𝗯𝗿𝗮𝗿𝗶𝗲𝘀: Optimized arrays, strings, regex, collections, and LINQ.

𝗜/𝗢 & 𝗖𝗼𝗺𝗽𝗿𝗲𝘀𝘀𝗶𝗼𝗻: Long path support, faster file ops, and Brotli compression.

𝗡𝗲𝘁𝘄𝗼𝗿𝗸𝗶𝗻𝗴 & 𝗝𝗦𝗢𝗡: HTTP/3 protocol support and lightning-fast JSON ops.

𝗫𝗠𝗟 & 𝗖𝗿𝘆𝗽𝘁𝗼𝗴𝗿𝗮𝗽𝗵𝘆: Efficient XML processing and new cryptographic algorithms.

𝗗𝗶𝗮𝗴𝗻𝗼𝘀𝘁𝗶𝗰𝘀 & 𝗘𝘅𝗰𝗲𝗽𝘁𝗶𝗼𝗻𝘀: Advanced event tracing and optimized exception handling.

𝗥𝗲𝗴𝗶𝘀𝘁𝗿𝘆 & 𝗔𝗻𝗮𝗹𝘆𝘇𝗲𝗿𝘀: Efficient registry ops and compile-time code gen.

For more details, check out 𝗦𝘁𝗲𝗽𝗵𝗲𝗻 𝗧𝗼𝘂𝗯'𝘀 massive .NET blog post titled 𝗣𝗲𝗿𝗳𝗼𝗿𝗺𝗮𝗻𝗰𝗲 𝗜𝗺𝗽𝗿𝗼𝘃𝗲𝗺𝗲𝗻𝘁𝘀 𝗶𝗻 .𝗡𝗘𝗧 𝟳.

So now, if you are trying to get your boss onboard with upgrading to .NET 7, you can say:

“𝘐𝘯 𝘢𝘥𝘥𝘪𝘵𝘪𝘰𝘯 𝘵𝘰 𝘢𝘭𝘭 𝘵𝘩𝘦 𝘯𝘦𝘸 𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯𝘢𝘭𝘪𝘵𝘺 𝘪𝘯 𝘵𝘩𝘦 𝘳𝘦𝘭𝘦𝘢𝘴𝘦, .𝘕𝘌𝘛 7 𝘪𝘴 𝘧𝘢𝘴𝘵, 𝘴𝘶𝘱𝘦𝘳 𝘧𝘢𝘴𝘵.”