The current package management frameworks already allows for that option.
The software vendor also has the option of providing a Windows style GUI installer. These have been commonplace since the mid 90s. The developer can also provide a self contained tarball.
The far bigger problem is the perception that the market is too small to bother with.
In general, downloading things from random sources doesn't seem to be where the market is going. Android and Apple are great examples of this. Furthermore, the old approach of downloading things from random websites doesn't always work out nearly as well as some people like to pretend. That's probably why the market is moving away from that.