BepInEx allows for easy integration of other Unity modding frameworks. That way you can get the benefit of installing only one framework without worrying about potential compatibility issues. Moreover, by using BepInEx to power plugins from other frameworks you get the benefits of

As of right now, BepInEx 5 has loaders for the following frameworks and tools:

Framework/Loader BepInEx Loader Status
BSIPA (Beat Saber IPA) BepInEx.BSIPA.Loader Stable, Supports most features
IPA (Illusion Plugin Architecture) IPALoaderX Stable, Maintained, Full interop
MonoMod Patches MonoModLoader Stable, Maintained, Supports most featues
MuseDash ModLoader BepInEx.MDML.Loader Stable, Maintained, Full interop
Sybaris 2 SybarisLoader Stable, Maintained, Full interop
UMod Framework BepInEx.uMod.Loader Stable, Maintained, Supports most features
Unity Mod Manger Yan.UMMLoader WIP, Maintaned by community, Full interop
UnityInjector UnityInjectorLoader Stable, Maintained, Full interop