Seriously, why it was not a problem for two centuries yet nowadays it's suddenly a new problem which requires a complex, electromechanical computer operated solution?
Don't get me wrong, I'm not defending the current implementation, but it makes sense to me to try and improve the world to make it more disability friendly.
I don't much care for the new "compliant" controllers though, not least because the sounds they emanate are quite unpleasant and often much less nice than the ones emitted by the door systems they replaced. Older hustle alarms, etc. sounded like they were produced by something at least slightly polyphonic, whereas all of these new systems seem to produce all of their sounds via an ear-piercing piezo buzzer only.
Besides the hustle alarm there's the sound to notify you the doors can now be opened (often not present on older, non-compliant systems, but now seemingly deemed required). I was always fond of the sound the Class 365/465 Networker used for this - an actual mechanical bell, which produced a pleasant sound. Of course it's now been torn out and retrofitted with an awful piezoelectric tone of the most ear-violating variety. It feels like nobody even tried to make these sounds pleasant, and probably went with a piezo buzzer rather than a mechanical bell because it costs less, and what hardware designer even knows how to integrate a mechanical bell these days?
The closest to not having a hustle alarm I'm aware of in the UK is for London Underground and DLR stock, which basically starts to play the hustle alarm at the same time as the doors close, making it a bit of a token affair.
Those interested in this sort of thing might be interested in this TfL report which actually studied in minute detail whether they should change the delay on the doors closing after the warning sounds. I encountered this once and was fascinated by the details. https://assets.publishing.service.gov.uk/government/uploads/...
BTW, the applicable safety requirements standard for power-operated passenger train doors is GM/RT2473 (or its predecessor on older rolling stock, GO/OTS300). Don't ask me how I know this...
