Is there a explanation? Yes

Is it reasonable? Not to me.

WHEN REMOVED FROM YOUR BAG, THESE ITEMS ARE MUCH EASIER AND FASTER FOR A T-S-A OFFICER TO SEE ANY SIGNS OF TAMPERING . IF YOU LEAVE FULL SIZE ELECTRONICS IN YOUR CARRY-ON BAG ADDITIONAL SCREENING WILL BE REQUIRED.

From their website.

They have always insisted some items be separate in a bin by themselves to get a better picture of them, and so things under or over them will not make it harder to see the contents.

I think they just like buying bins.