When an amendment is proposed why is it not sent to the president?

 Amendments must be ratified by the states.  They do not become law with the signature of the President.

Explanation:

Bills passed by Congress become law with the signature of the President.  Amendments to the Constitution, however, require a more stringent process.

An amendment must first be approved by Congress and then also must be ratified by the states.   An amendment must be approved by a two-thirds vote in both houses of Congress, and then  three-fourths of state legislatures then must ratify the amendment  in order for it to become a part of the federal Constitution.

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