Both Wild World and New Leaf added the possibility to change the in-game clock without the need to change the system's clock for two reasons: they're on portable platforms, so they expected people to travel between places with different timezones (as you stated), so that makes it easier for people to play synced with the timezones they're in. Also, and probably more important than that, it was implemented as a way for people to be able to adjust the game's clock to account for Daylight Savings Time without spoiling turnips and other things (this is clear in NL, for example, as you can do that when you load your game and talk to Isabelle).Time travel
Time travel, often shortened to "TT", is when the player manually changes the time of their game to benefit from seasonal events, bugs, fish, moving villagers out, moving villagers in, upgrading shops, progressing story, etc, in their Animal Crossing series games. It is also used to manipulate...animalcrossing.fandom.com
Like I said, we used to have a phone in our house where we could call and change the time inside the game while your save file was already loaded.
I guess the mechanic is more about changing your timezone, but it is still technically considered time traveling.
But it was never there as an intended game mechanic. The devs later on added dialogs joking about TTing because the players would still do that and for the devs, it wasn't a problem at all, and this is why they never prohibited TTing even if they could do it if they really wanted to.
I have no problems with people who TT, the same way I never had a problem with people using the Konami code to beat Contra back in the day. I just call it what it is, a cheat, or in AC's case, an exploit (would be the correct term).
There's a lot of ways to exploit games, and AC has it's fair share of exploits, like TTing and duping items. The problem I have is when people abuse these exploits to harm the community and it's players (often by scamming, as I don't think making more items available on the market is a bad thing, as it makes items more affordable since the supply gets higher than the demand).