Some say that Adam ate the fruit to protect Eve - and to die with her.
Personally, I do not see any of that. Who had been delegated authority to manage the garden?
Adam.
Where was Adam?
WITH Eve.
Adam abdicated his appointed "management" role, he abrogated his assigned responsibilities, resigned his role of head of the family, and allowed Eve to take the leading role.
Everything that darkness touches becomes a mess, a twisted, disfunctional operation - as we see in politics, science, families - destroying the good order that YHWH designed in the first place. A sober warning as to the contagiousness of evil - a very brief interaction with perfect man, a moment of letting down one's guard - and the whole of mankind dropped into a dark abyss..
And a sober warning for missing husbands and fathers - super disfunctional families. Also in Churches and ecclesias - note that the SAME instructions are given to presbuterious as to Adam...
But there may be a more sinister reason why Adam did not interfere...
He may have used Eve as test whether YHWH would strike her dead or not - as he desired that experiential personal knowledge of EVIL.
He had all the knowledge that man ever needed - he had enough brain power to name ALL animals - something that needs thousands upon thousands of scientists today.
Adam did not NEED to have that evil knowledge.