If a rental unit cannot reach reasonable modern standards, the landlord should not be allowed to rent it out until it does. The idea that some building standard from decades ago will meet modern needs and that the landlord/building owner has no responbility to modernize is absurd. Its like saying a unit with asbestos is adequate cause that was the standard when it was built.
I mean, it IS adequate in most cases. Removing asbestos is a last resort. It's not harming anyone in the walls, but it has a potential to do so if you try and rip it out.
I think the biggest factor here is the cost in safely removing it. Sure its not harming anyone in the walls, but mice may still stir it up and spread it around the building, and you'll never want to puncture the wall to hang a picture or a shelf. It is considered adequate because the exposure is so low, you would have a hard time proving it was specifically the asbestos that caused health concerns.
So long as asbestos is not (and will not be) disturbed, it is fine. The problems with it arises when any sort of alterations or renovations are needed.
A place I used to live in had asbestos-lined linoleum on the floor. It was 100% safe until the sewer backed up and flooded a bit of the area. When the old lino needed to be removed, it became a risk and required remediation. Until then, it was inert/fine.