The biggest problem is that few people actually read the warnings. Instead, they pick up on what the media tell them (by definition, guarannteed to be inaccurate if not and out and out lie) or just assume - for example - that because they live in Birminghams and there's a warning for the Midlands, then there is a warning for their back garden (in fact, the warning applies only to the Peak District) ...... And even fewer understand them.
They could try just issuing warnings to authorities, rescue services etc and others who actually know what they mean. But then, as we see with the health warnings issued on behalf of the NHS when there's hot/cold weather, they still get picked up by the media/public and are entirely misunderstood .....
Until the Met Office are able to issue the back garden specific forecasts that the majority of people seem to think they are already issuing, they really are on a hiding to nothing.