Why are relationships limited to two degrees?
The &quot;why&quot; question is fairly straightforward in an open source, community supported and community developed software world: because so far no one wanted more levels badly enough to develop or fund the development of an extensions for it :-)
But I would certainly recommend playing with the extension that @petednz recommended, and check if you can achieve your requirements.
And obviously you are very welcome to develop/fund the development of an extension that introduces more levels.