The usual progression that I have observed - in
all walks of life not just air transport:
- Something goes wrong and people die.
- The boffins come up with a safety procedure/device.
- The politicians respond to the newspapers by mandating this with the (near useless) cry that this "must not be allowed to happen again."
- Device and procedure is mandated.
- Years pass.
- Nothing goes wrong and this particular failure does not happen again.
- Years pass - decades sometimes.
- Folks talk about removing the device and/or procedure.
- < fill in the blanks >
- 'It' happens again.
- More people die.
- In the inquiry it is found that numerous voices in the company had been warning about the problem but they were ignored. In the USA you can start with Shuttle Challenge rin 1986. In the UK, you can start with the Kings Cross Tube Fire of 1987. Both of these were unique 'new' failures but are well known examples of the ability of people to ignore facts.
Very often, to be fair, this happens because each emergency has so many variables that you cannot plan for all of them. Modern world pax (particularly USA) want everything guaranteed but in life - It Ain't Necessarily So ...
With US 1549 they had more than just a fine crew, they had a river to hand that was ebbing and made it look (in the pictures) like a lake - if it had been in flood, then there would have been choppy waves and pax would probably not have been able to stand calmly on the wings. Indeed, if the water surface had been very rough, the a/c might have put her nose under very quickly and dived.
Removing life jackets? Someone will. My own view is that, in local waters then they are a real life saver. In open water, the event that brought the a/c down probably precludes their use.
When talking about weight and cost, don't forget that carriers have successfully resisted installing misting water sprinkler systems - but still sell heavy flammable bottles of alcohol!