The problem seems to me to be a complete lack of personal responsibility, more than common sense.
I spill a hot drink, I think “what an idiot, must find something/someone to help clear it up”. I don’t complain to a train company for inadequately warning me.
There is absolutely a phenomenon of over warning people and therefore the warnings having no effect. Some fairly terrifying examples of fire alarms set up so badly as to respond to a waft of hair spray or steam from a shower, meaning many interviewed in the recent student accommodation fire in Bolton said “I thought it was just a false alarm” when in fact they were in real peril.
I am quite certain the majority of people with reduced mobility have spent a lifetime battling a world not designed for them (and there is a rich irony in train companies pompously announcing this stuff when they can’t get the legally required adjustments to their stock correct a decade after they were instructed to do so). It seems incredibly patronising to suggest without such voice announcements every blind person would be hurling themselves down the gap between the train and the platform.
Some people will require assistance on, in and off trains. It might be inconvenient for operators to offer actual help, but it’s a lot more effective than barking incessantly at everyone in a patronising manner.