Right, I’ll follow your suggestion and ask by email. The blog looks very professional, and I think he’ll be able to answer my question well. Thanks for recommending
Discussion
post the answer
Don’t rush. I still haven’t gotten an answer, lol.
I asked that person about the question, and he also didn't think there was any particular reason it had to be that way. It seems likely to be one of those things in Bitcoin’s history that weren't technically necessary, but were simply implemented by Satoshi that way—and now it can't really be changed, so it's just left as-is. Looks like my guess was right.