Yeah, it's not what you'd call "fun" much of the time but it's quite addictive and the social side is very well done (which is probably part of the addictiveness as we all crave other people's approval!).
It's certainly a different experience, the music is exceptionally well chosen, really does make those long trudges pass quicker and become almost meditative at times.
Yes, as I've said a couple of times already, I can't exactly put my finger on why this can be tedious and fun at the same time. As you say, the social side plays a part in it for sure, the feeling of helping others and watching things grow is really rewarding. It has excellent music and presentation, very high production values as well and that also contributes. Maybe there's just something exciting in trudging through those landscapes with heavy cargo struggling for balance, caring for your equipment and avoiding dangers. There's something rewarding in those journeys, especially knowing that completing them gets you more resources/equipment/likes etc.
Sure, there's no pew pew every 5 mins nor big bombast explosions and it is based on repetitive walking but I somehow don't mind.
There's a lot of surrounding systems and details that you won't catch a glimpse of the entire thing on YT but at the same time I can't picture this becoming appreciated by the majority.
All games are repetitive at heart, it just boils down to liking a particular gameplay loop.
It's the weirdest thing I've played in years, tied with Nier Automata which landed on my list as one of the most memorable and clever gaming experiences ever, so I don't mind.