I lived in tropical areas...but growing up I am so used to Christmas is in winter and April is the Sakura season, so I just choose northern hemisphere.
You're the first person I met who did this too, at least for the same reasons ^^
I am from Australia, but I've played this series for 16 years or so, so I'm just used to it, it's tradition and I liked the NH event calendar... especially since it doesn't snow where I live or anything, it's not like the weather matches anyway.
Sometimes I think it was silly, because SH stuff is very in demand, but I'm glad I did it to be on the same page as other NH players, plus my brother plays in SH anyway. And I got the mush stuff by trading ^^'' I just feel comfortable this way. And it's nice to have the days be longer and sunnier when it's cold here, and frosty when we're having heatwaves...
Do Australia, New Zealand, South Africa, and South America even get the full seasons to take advantage of it?
I don't know what this means... do you mean, do SH players get winter etc. in game? Of course they do. But - maybe this is what you meant - the updates seem to be geared more around Northern Hemisphere players so far, in my opinion. We'll see, as the games move into summer and winter, the differences will be more pronounced. My understanding is that, for example, Wedding Season won't be in June for SH players (because Wedding Season is a summer event). Autumn Moon wasn't in the game at release (fun fact, the actual date was the release date - March 20 - so we could've seen it on midnight release), but they might add it in closer to autumn in the NH, since it's an event that's been in nearly every game. But that's one reason I don't regret playing in NH. I don't want to play seasons without the content patched in :/ I hope they will add a good amount of events for both.
In the game at base, there were two autumn things already (mush season + maple leaves falling), plus Snowboy was in as well, and Christmas DIYs for the winter season.
If you mean our irl seasons... well, the seasons are very different everywhere. In a huge continent like Australia, we have lots of climate systems. The indigenous nations here kept our own calendars based on the unique weather in Australia and the behaviour of plants and animals endemic to our own land. There are parts of Australia with a monsoon season, for example. Climate variation is very normal, we have wet autumns and summers and dry winters and springs, but that's not true in plenty of places.