Also, it is one of the areas (in the US) where formalities matter a LOT. There are no magic words or special tricks you need to know to enter into most sorts of contracts and make them legally enforceable (it is a matter of intent rather than the application of magic conjuring words), but when it comes to T&E courts are dead serious about observing the required formalities since by definition the testator won’t be around to explain themselves when the rubber meets the road. Plus it‘s a matter of state law, and each state’s rules and requirements are different.
Similar, and when real property is involved in the trust it involves changing the title too which is an exercise in drafting and then the associated legal fees. What on the outside seems like just switching a name is on the inside a pig!