It wasn’t that things were very different on Earth, not when you got down to the bare bones of it. There was still love and hate, dating and war, friendships and prejudice; they may take different forms than on Mars, but they were still around. So it wasn’t that life on Earth was inherently different from life on Mars, it was more that there were just a whole new set of problems for M’Gann deal with when it came to life on Earth.
For example, regular everyday people tended to be freaked out by the shapeshifting thing. Or there was the fact that there weren’t a whole lot of telepaths on Earth and the whole planet had apparently come to the collective agreement that using that gift was rude, whether they could control it enough to not go digging through other people’s personal thoughts or not.
But the absolute worst problem of all was making sure every second of every day that none of M’Gann’s teammates ever found out about what she really was. She’d seen enough Earth television and movies to know what would happen if they did and there was a decent amount of self-preservation involved in the decision. But really? She just didn’t want to lose all of the wonderful friends she’d made.
Real, true friends that cared about her and protected her no matter what.
But who really wanted to take that chance?