The single biggest reason. Hundreds of essential mods—like .NET Script Framework (used for crash logging and advanced modding), No Grass in Objects, and certain animation frameworks—were never updated for AE. They only run on 1.5.97.

AE forces you to download four free Creation Club mods (Survival, Saints & Seducers, etc.). The USSEP for AE includes hundreds of patches for these CC mods. If you don't want those mods, the AE USSEP will still check for them, leading to errors. The USSEP 1.5.97 is lean. It fixes the base game and nothing else.

Works with:

Does NOT work with:

If a mod requires newer USSEP:
You can try to manually backport USSEP changes, but that’s advanced. Easier: find older versions of those mods or stay on AE.

While the Anniversary Edition includes dozens of Creation Club addons, the Fishing system was the headline feature developed directly into the core game update (1.5.97), accessible even to players who did not purchase the Anniversary Edition upgrade.

Feature Details:

A common argument is, "The AE update was years ago. Just update." Let's address that. While many major mods (SkyUI, USSEP, RaceMenu) have been ported to AE, the niche is lost. The longevity of the USSEP 1.5.97 ecosystem is proven by the "Downgrade Patcher" itself, which has over 2 million unique downloads.

Furthermore, Bethesda has a habit of breaking things again. With every minor Steam update (1.6.640, 1.6.659, 1.6.1130), the AE USSEP requires a recompile. The 1.5.97 version is static. It will never break again.

USSEP is a community-driven project; its releases reflect ongoing volunteer maintenance. A 1.5.97 release signals active patching in response to official updates and community-reported bugs. Users should consult the USSEP changelog and discussion threads for details on specific fixes and reported issues.