Or is it because nobody wants to assume responsibility?

Let's say what you really want is to be able to fix simple stuff ( replace easily replaceable parts ), and get the experts in for tricky stuff. However the contractor, who now isn't fully responsible to changes to the system, now insists that you take the full risk of your repairs ( perhaps even saying they will void any warranty if you touch the oven/lift ).

Then faced with that nobody is brave enough to say - heck fine - we will take that responsibility.

And so because the lawyers were prepared to take that risk, the people on the boat are infantilised by contract.