Kids, especially teens, never like being uprooted but sometimes, for career or financial or school reasons it's necessary in ways that they cannot always appreciate at the time. But at least they are still with both parents, or their sole parent and moving for reasons that benefit them and the family, not just because one parent is chasing a new relationship which may not even last. That's the difference.
Being lumbered with step parents and step siblings you don't like and didn't ask for can cause lifelong trauma. Especially when you are expected to live with them full time and no-one ever asks how you feel about it. Or if they do, they are only going through the motions of asking, so they can say they were not selfish and approached it 'responsibly.' But actually, they are going to dismiss how you feel as 'silly' and ignore it regardless of how you say you feel. As I said, sometimes it works out fine, but often it doesn't.
My stepsister absolutely adored my dad. Of course she did. He was charming to her. She never knew her real dad . She was crying out for a daddy figure to attach herself to. My dad always had commitment and responsibility issues and was a lousy, flaky, largely absent father in the same way that he was a lousy, flaky, largely absent husband. But he was a charming and persuasive adulterer and I think he applied the same qualities to step-parenting. It was easy to be a great stepdad because it didn't come with much expectation or responsibility, unlike being a real dad.
I swear my stepsister actually had what amounted to a crush on my dad, who came into her life when I was 7 and she was 8. He could do no wrong in her eyes. He was a much better father to her than he ever was to us and she got the best of him. My stepmother made sure of that. To us it always seemed that he treated her like a little princess. My siblings and I saw that and felt it deeply. We had to watch her calling him dad and draping herself all over him, when we only had very sporadic contact and didn't feel comfortable with draping ourselves over him because he always seemed more like a distant uncle than a dad. It didn't feel normal or natural. It damaged us. Our stepsister wasn't all bad, she just had the bad luck to have a grabby, manipulative bitch of a mother who was on the lookout for a meal ticket and got herself 'accidentally' knocked up at the very first opportunity, before my mum (and we) even learned of her existence. In fact if she hadn't got PG the affair may have fizzled out and my dad would have probably moved on to the next girl in the next port, as was his way. But she made absolutely sure my mum found out about her. She wasn't going to leave it to chance or wait for him to leave of his own accord. She knew what she wanted and she made sure she got it.
You see, this is the same family, the same kids involved but with very different memories of how it felt to be part of that blended family. You could listen to my stepsister and think it was all easy and wonderful. Well it was. For her.