Why would principled members of Congress cosponsor and vote for the term limits resolution if it meant they would have to leave office perhaps at their very next election?
The resolution includes an important section to ‘grandfather in’ current members of Congress for the terms they have already served. Here’s the relevant text in Senator Ted Cruz's and Representative Ralph Norman's term limits resolution:
SECTION 3: No term beginning before the date of the ratification of this article shall be taken into account in determining eligibility for election or appointment under this article.
This language is based on historical constitutional precedents in the 17th and 22nd Amendments. In the 17th, which changed senators from being appointed by the states to being elected, the amendment included similar language:
“This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.”
The 22nd Amendment limited the president to serving no more than two terms, but exempted the incumbent president:
“But this Article shall not apply to any person holding the office of President when this Article was proposed by the Congress, and shall not prevent any person who may be holding the office of President, or acting as President, during the term within which this Article becomes operative from holding the office of President or acting as President during the remainder of such term.”
The exemptions that ‘grandfathered in’ sitting senators and presidents were important in gaining the votes for ratification.