Yelena might not be familiar with the world Mikasa came from, but she did know how to entertain herself without the usual modern trinkets. She would agree that most people took most things for granted. She didn't grow up with a lot at her disposal, but she didn't feel badly about that. Clearly there were some with still less.
"Yes, I find there's a lot of that in a modern kitchen. Appliances and tools with only one use. Like an apple corers." Yelena shook her head. "When there are perfectly good pocket knives."
So her friend Erwin was not so dissimilar with her sister's situation. If he went back to where they came from, time would simply flow on and he would die. Like Natasha, he had motivation to stay here.
"I was still alive, where I came from. Not about to die, as far as I know. But my sister, Natasha, she died in our world. She's here now and safe. I'm not sure I would want to leave her again."