Because it's absurd and violates physical laws. Just as I don't think Indian shamans can actually levitate. And no, Uri Geller cannot bend spoons with his mind.
All of these goofy magical claims go on the same shelf.
Of course you are right, but you are basing that conclusion on the irrational things "believers" claim like the literal rising of the dead from graves, but thats not the subject of the resurrection.
Its like if someone was deceived by nazi propaganda thinly veiled as christian white nationalism and was awakened to the evil of those "beliefs', renouncing them as such which is exactly like the dead coming back to life or the insane being restored to a sound mind. It happens all the time.
The resurrection was never about the resumption of a former existence. It was always about entry into a new existence like a child becoming an adult, or the dead becoming a "living being".