I know that the very early version of the Bitcoin code had a lot of advanced features, and was already very mature.
But Segwit (storing signatures separately from the transactions in the block) is a very simple change, and so obvious that I'm sure it must have passed Satoshi's mind many times.
So I'm wondering: what could be a reason that Satoshi choose to store the signatures inside the transaction? There is always the possibility that he just made a stupid mistake in the design, but I find that hard to believe.