Because you have to read docs, and do more stuff manually.
Some of us tend to choose directly specialized systems, that have been built for home automation specifically. I consider this as a more specific approach. Because you have to read docs, and do more stuff manually. But these softwares are often open source, supported by a large and involved community, and you'll find help easily. However you are your own customer support :) Don't be afraid, there's a ton of Modules/Quick Apps/Plugins, and you can easily connect your assistants, or brand systems, like Nest or Hue into these open-source softwares.