> More corrosion
Surely given starlinks 5ish year deorbit plan, you could design a platform to hold up for that long... And instead of burning the whole thing up you could just refurbish it when you swap out the actual rack contents, considering that those probably have an even shorter edge lifespan.
Starlinks are built to safely burn up on re-entry. A big reusable platform will have to work quite differently to never uncontrollably re-enter, or it might kill someone by high velocity debris on impact.
This adds weight and complexity and likely also forces a much higher orbit.