Biden never said he supported full legalization as far as I am aware, so it's not surprising he didn't go as far as he could.
She just made the announcement for the first time in this campaign, so not stated that yet, but she has pushed for legalization via legislation in the past as a senator and called for faster action for the DEA on rescheduling as VP
In other areas, Walz and Harris have already given plans for passing legislation to make banking access easier for legal states and helping veterans get access to medical marijuana in the VA
He never explicitly said he would be a one term president or necessarily saw himself as one. I looked back to double check again, and he only made cagey statements about seeing himself as the transition between generations. A two term president could still qualify for that. The more explicit one term stuff was from his aides saying he was considering that
Should he have just been more direct, yes, but what he said was nothing as explicit as directly stating we need marijuana it to be legalized