Tesla sells their own branded panels and monitoring solution, and do the installation.

Other installers might sell you LG panels and Enphase inverters and LG batteries, and then your monitoring comes from whomever, and the installation warranty provided by the installer.

So, no matter who you choose as a vendor, the parts are typically made by several different companies, and someone needs to install them and provide support.

I assume people who use Tesla as their middleman vs some other middleman do so for branding, monitoring, whatever reasons. Maybe they like the complete solar+powerwall battery+app solution. I don't know.