I get it, totally, and I spent a lot of time in my career explaining that risks cannot be completely eliminated from any human activity. The problem is that you run into the infamous situation in which Ford reportedly calculated the cost of fixing millions of Ford Pinto fuel tank shields and weighed that against the probable cost of the lawsuits that they expected to be involved in as a result of the foreseeable number of fires that they expected to be involved in, and determined that it wasn't worth doing the repair. The general public - and the lawyers that they hire! - don't understand this, and frown on viewpoints like that.
Having a fixed fence or handrail a metre or so back from the platform edge, with openings roughly lining up with where the doors on the subway are, isn't a terrible idea. Reason for having it a metre or so back: (1) maintains an escape path for someone who accidentally gets into a place where they shouldn't be, (2) maintains some flexibility for where the subway comes to a stop - the braking system was never intended to be precise - if it accidentally stops a little too early or late, people can still get on and off, (3) avoids the edge of each opening in the fence being itself a crush point against the moving train if it were positioned too closely.
Common sense is all too uncommon. This solution probably won't happen, because it isn't "perfect". Perfection is the enemy of the good enough.