Trying to secure a common residential building with fobs for every level is a fool's errand. It creates more problems than it solves. Those systems need constant babysitting to maintain working at every door. Most residents aren't going to report a broken one or malfunctioning one they will assume someone else is doing it. Scheduling the company to come out and fix the fob mechanisms gets costly so property management will largely ignore things like staircases to eliminate having the repair company come out weekly. Some maintenance contracts are priced per visit while others are just a flat fee so it varies what deal a property will have. Then throw in the replacement parts game you play where the repair companies don't usually have some warehouse of parts gathering dust. They keep some things around and the rest they order when they need it. Plus changes in parts as the manufacturers recall, replace or upgrade systems and buildings that mostly have no desire to replace that system on an ongoing basis. At the end of the day, most property owners are not going to expect to ever have this kind of security threat. Trying to keep people off other floors is overkill anyway. Residents at most buildings I have ever lived in hang out with each other all the time and need to move between floors without getting approval from the leasing office.
The fobs in some ways are more security theater because unless its the federal reserve they just don't get the attention to maintain a secure exterior envelope let alone an internal one.
My roommate leaves our front door unlocked all the time we have argued about it because he just doesn't think its a big issue and thinks I am making a big deal out of nothing. He goes to bed with every light on in the apartment not because its some sort of strategy its because he doesn't care. It's annoying but its the reality that some people are just raised not to think about those things.
Something tells me a stronger fob system here probably wouldn't have stopped this from happening anyway.