Ah yeah. The "why" with a lot of the porcelain stuff probably tends to be an unsatisfying "Because somebody didn't think it through very much a few years ago." git-reset would probably be better if it defaulted to --soft, and possibly left the other options to other commands.
Branching/merging/committing is pretty straightforward. The problem is that some commands seem to be very convoluted. For example, why does reset do four different things depending on whether it's soft or hard or plain? I keep having to Google to find how I can revert my latest commit.
Another thing I have trouble with is obscure failures. Obviously this isn't something I can just learn, but there are times when git fails for a reason I don't understand...