Well, by the same token we could ask why did we need a body to begin with! But we know that Adam's 'personality' is not known, nor was it something God cared to talk about.
Adam and Eve were supposed to live in bliss. The only thing God ever told them is "multiply!" The personalities begin to emerge in the fallen state, when Cain slays Abel out of jealousy, and later on as some are deemed righteous (Noah, Job, etc.) compared to others.
The answer to your question is simple: we need bodies because that's how God created us! That is our "normal" state. If He wanted us to be noëtic beings without bodies we would be angels. He already created those. He also created animals, although He wanted us to eat herbs! [this is all assuming the story of Genesis is not a myth]
Most importantly, no one is saying that we will not be different as we are today; the most important thing is that our personalities will not matter, as Adam's didn't matter. Every snow flake is unique too! Does that make each one of them precious? They all equally 'populate' the area they fall on, their uniqueness notwithstanding.
Angels are also unique and different, but their individuality and 'self' do not matter; what matters is why they appear and what message they bring. They only do God's will.
When we die unto oursleves, our personalities do not disappear; they become irrelevant, which is as good as disappearing; none of our iniquity obstructs His light. Because from there on we exist only to obey and carry out God's will. No ours. We exist for God, not the other way around.
Here's my story of why we need bodies:
(1)It's so I can tell us apart. I'm "in here" and you're "out there". (Yeah, and I'm the good looking and smart one, too. Hmm I see the codeine is kicking in ....).
(2) It's so I can tell you from someBODY (nyuck nycuk) else.
(3) And it's so we can communicate. My body does things to the air, and the air does things to your ears, etc ....