P2P filesharing is part of the "decentralised web", and people seem to have no trouble installing the software for those.
Now consider how complicated installing on a server is in contrast. Upload you files to a folder or directory, enable permissions, set configurations not just for your server but also the language the program is written in - the list goes on.
I think a lot of the difficulty is artificial, created by software that is far more complex than it needs to be, to cover far more use cases than most users actually need. In the "enterprise" space, a lot of this complexity probably also drives auxillary revenue in the form of training, consultancy, etc. In other words, it could be a deliberate barrier to entry. Building big, complex, immensely flexible, yet difficult-to-configure systems with plenty of dependencies just seems to be the norm.
Perhaps some in the tech field would like to keep it that way? Would Saas be less attractive if installing a self-hosted solution was simple, easy, quick and secure?
Indeed, the whole category of "enterprise software" often fits this business model.
But me and many others have written HTTP and FTP servers which do not require any installation at all --- they're just a single (often very tiny compared to most other software) binary, sometimes with an optional configuration file. If you're doing something like hosting static pages, this fits the use-case perfectly well.
Finally, a huge part of making the web truly decentralised is to abandon the notion of dedicated servers/clients altogether --- and thus also the notion that you must need a dedicated or "server" computer to host anything, or for that matter a dedicated Internet connection. Of course some machines will have more resources to serve, and a typical residential connection may be more limited, but the key idea as exemplified by P2P is that any machine can serve.