Because the changes would likely require a Constitutional Amendment. For setting a term limit, Article 3 of the US Constitution establishes that judges serve while "in good standing". This has been interpreted as meaning "for life". And this interpretation has some pretty strong backing from Hamilton's writing in The Federalist Papers No. 78. While the Federalist Papers do not, technically, have legal standing in the US, they are often used to fill in the gaps left by the imprecise language of the US Constitution.

Enforcing a code of ethics is probably a muddier situation. Article 3 establishes that Judges serve during "Good Behavior". But how is that defined and who gets to define it? Technically, The House of Representatives can impeach a judge (and this has happened in the past). So, the Legislature could simply say, "we'll impeach judges for violating this list of things". At the same time, an impeachment is not self-executing. So, a judge would not be automatically fired for violating one of those things. At best, the list would be a guideline and the sitting House (at the time of the impeachment) would have to draw up and vote on articles of impeachment. Could the legislature pass a law making the removal of a judge self-executing by defining "Good Behavior"? Maybe, though the same Judaical Branch whom it would affect would be the one to make that decision. I strongly suspect they would say, "no". And that may not be the worst outcome.

In Federalist No. 78 Hamilton makes the argument that the Judiciary must be very independent from the Legislature and Executive branches to avoid becoming an arm of those branches. The claim is that the Judiciary must be free to judge the actions of the other two branches, and rule purely on the Constitution and the Law. If the Legislature and Executive get to start tinkering with the tenure of judges, via rule making, there will be some incentive for the Judaical branch to begin serving the will of the other two branches. That's fine, if you agree with the other two branches, it's less so when you don't. In the end, I suspect that an enforceable code of ethics is going to require a Constitutional Amendment as well.

The changes to Presidential Immunity are probably the worst one to evaluate. I'm convinced that this decision was very much the court picking a position and then papering over all the hideous gaps in it. Unfortunately, because the Judiciary is the final arbiter on this one, and they say the decision is based on the Constitution, any change will have to come as a Constitutional Amendment. I recognize the circular nature of that logic, but that's kinda where we are at. Unless and until the make up of the Supreme Court changes, Nixon was right.

And for fun irony, the US President is actually not involved in passing an amendment to the US Constitution. That process takes 2/3 of each House of Congress and then 2/3 of the States. The President doesn't get a chance to veto/sign the Amendment. And, that has about the same chance as a snowball fight in Hell of happening right now. So, everything around this subject is just useless posturing. Nothing is changing any time soon.