Modern buildings are built with partitioning - so if a fire does break out, it's contained. You have concrete floors, risers with fire proof floors and sealant, and fire doors everywhere; along corridors, to flats and to risers. Lift shafts are concrete lined, etc. Plus of course you have fire detection systems.
The problem when a lot of older blocks is that these systems are compromised by people living there - cutting through fire partitions, riser cupboards being left unlocked (or used for personal storage), corridors with fire doors propped open, doors replaced with a standard front door (or worse, internal door), so the protection it offers is poor at best. A stay put policy is definitely the best policy where these things are in place but if they're not, then it just means that people are waiting to die and it allows the fire to spread - particularly if there are personal items left in corridors which should be 'sterile areas'; I.e nothing in them to burn.
And retrofitting a bells and whistles fire detection system is prohibitively expensive. Like, hundreds of thousands of pounds expensive. Which is fine if you have the money but councils often don't, and private residents often won't pay for it, they make the decision not to.
Fire detectors should be tested weekly, with risers and associated equipment tested 6 monthly. I would be surprised if this has happened, given the issues they've had with controlling the fire.
I was a freehold property manager before I became a SAHM and the idea of a fire terrified me - both on a professional and a personal level. I'm extremely cautious about having doors shut and working smoke detectors at home. My heart goes out to everyone there, it's horrendous. I only hope that it isn't as bad as it seems.