a)

'However, there are signs of disquiet in this vast, global industry. The sheer volume of sport is reaching bursting point for all but the most besotted fan. ..........'

In the previous text, what is the meaning of 'all but'?

In my dictionary, is written : 'all but = nearly'

If ever it means 'nearly' here, what's the point of putting 'nearly' & 'the most' together?

The sheer volume of sport is reaching the bursting point for everyone except the most besotted fan.

The sheer volume of sport is reaching the bursting point for nearly everyone.

(I think it doesn't make much sense in my native tongue. Does it in English?)

Yes. But it takes some getting used to.

And by the way, the word 'for' means 'because of them' or 'in their point of view' in this context?

in their point of view

b)'S.m.u.t Filter Blocks All But S.m.u.t'

'S.m.u.t Filter Blocks Everything But S.m.u.t'

'S.m.u.t Filter Blocks Everything Except S.m.u.t'

'Bush's Poverty Talk Is Now All but Silent'

'Bush's Poverty Talk Is Now Almost Silent'

'Bush's Poverty Talk Is Now Nearly Silent'

Is it all the same here? If it means 'nearly' in the 1st sentence, why not say 'S.m.u.t Filter All But Blocks S.m.u.t' since it is an adverb? You could say this, but the meaning is a little bit different. The second phrase puts the emphasis on what the filter does. The first phrase puts the emphasis on what is blocked.