The issue is Modding is too entrenched for SE to do anything about without a huge community backlash and a financial hit, plus if they need to block third-party tools they would need to add an invasive anti chat would cause even more of a backlash.
Plus something that isn't talked about is that it isn't little jimmy still going through Hevensward that uses 3rd party tools. it's going to be a lot of your endgame players who have been here for years and keep their sub rolling month to month and I don't think SE would want to lose a good chunk of their core community over modding.