It is true that the Budapest Memorandum does not create a legal obligation for the signatories to provide military assistance to Ukraine. If it did, we would have committed massive U.S. combat troops in Ukraine, not just provided weaponry.
But at the least, it certainly provides a clear legal justification for us to provide Ukraine with weapons with which it can defend itself.
Kind of like a "Stand your Ground" law. You're not obligated to stand your ground, but if you choose to do so, you're perfectly justified in doing so. Which renders ridiculous any claim that providing such assistance to Ukraine is an offensive provocation against Russia.
It should also be remembered that Russia itself was obligated to respect Ukraine's borders, and itself clearly breached that Agreement.