Unfortunately they make all of these things ridiculously complex and technical, creating whole industries that shouldn't be required.
Things just evolve this way. There is no 'they' who sit down and say lets make trusts more complex. In fact the opposite, the government is conducting a review of trusts in an attempt to make things more straight forward (but this will probably only make things more complex).
But the same can be said about personal ownership of property. There is probably more caselaw in this regard. Bankruptcy, priorities, family law, succession law - family provision and notional estate orders, taxation etc. Its all very complex.