Because Microsoft delisted Midtown Madness 3 from the Xbox Marketplace in 2016. The only legal way to play is via an original disc, but modern PCs lack disc drives and Xbox hardware. Thus, the emulation community has kept the ISO alive.

Midtown Madness 3 was released exclusively for the Xbox and never received an official PC port, you can still play it on modern PC hardware by using the original Xbox emulator. Playable Options & Required Files

Once you've downloaded the torrent ISO file:

The original Xbox Live service is no longer active, but you can still apply updates and DLC: Midtown Madness 3 | xemu Microsoft Xbox Emulator

: No official “settings update” exists. Community emulation patches can adjust FOV, texture filtering, and widescreen support.

Unlike Midtown Madness 1 & 2 , which run natively on Windows 10/11 with simple patches, MM3 was built on a proprietary Xbox graphics pipeline. No source code was ever released for PC.