If a device manufacturer could count on you having VPN access to your home network they could make it trivial to set up and use. You’d open an app or visit a URL, log in, and you’d have access.
If it's in an app, then maybe they can rely on your phone already being in the VPN. However, if it's in a website, then you have to give them access to export the footage out of your network and into their third-party servers (you can't expect the customers to configure and host an HTTP server from their network). You lose the advantage of the VPN (in this scenario) then. From a typical customer's point of view, it's better to be able to access their stuff from a website than from an app, because they can access their stuff from more devices without prior configuration. For example, they can borrow a friend's laptop to see the footage without needing to get them to install or configure anything to get into the VPN.
I think that any solution that includes a VPN is going to lose out in convenience even slightly against a solution that doesn't, and in a market where convenience and ease of use goes above all else, it would just not work.
If a device manufacturer could count on you having VPN access to your home network they could make it trivial to set up and use. You’d open an app or visit a URL, log in, and you’d have access.