Hard coupling to a framework-specified details is tough to remove after the fact. For example, everyone's OK with ActiveRecord's coupling until their test suite

Hard coupling to a framework-specified details is tough to remove after the fact. For example, everyone's OK with ActiveRecord's coupling until their test suites are slow. This decision creeps up on them and they have to expend additional energy dealing with it. It's the tradeoff of simplicity: framework authors want to make things easy (and this is commendable).