Why should I use?

Because,

    It is open source.
    It is fast.
    It is lightweight.
    It is modular.
    It contains the CurseForge, Modrinth, and the OptiFine APIs. *
    It is built with a useful and efficiency-based UI.
    It includes the most used modding APIs like Forge and Fabric.
    It supports CLI.
    It has its own Java Download Manager.
    You can download multiple modpacks in one profile.
    You can see your worlds (including seeds, game mode, and worlds' spawn point), and resources (mods, resourcepacks, modpacks, and worlds) on one page.
    You can easily back up, import, and share your profiles and worlds.
    Also, it supports offline and online authentication.