What is different about LES tenements today?

I’m doing a research paper about governmental neglect of immigrants and working class people during the Industrial Revolution.
Don’t worry, this isn’t a homework question.
During the Industrial Revolution and Gilded Age, the Lower East Side of Manhattan was the most densely populated place on the planet. Tenements were constantly at risk of fires, and the people were at risk for diseases from living so close together. 1 in 10 infants died in urban areas because of the dense living conditions.
The tenement buildings (though not disease-ridden) still exist today.
What changed that makes them less at risk for fire and disease, and why are they so sought after to live in today, when people hated living in them because they were so packed years ago?
What am I missing? Modern technology has helped us somewhat, but don’t the basics still remain?
I don’t need this info for my paper, I just want to know at this point. What changed about these tenements? New York City is still one of the densest cities in the world, just as it was during the Industrial Revolution even more so now. The apartment buildings are just as packed. What happened?