1/2/3. Insulation, Energy, Aesthetics
4. Cost
5. Material that doesn't burn up and torch people when it catches fire...
Since you're just guessing ("I think"), my guess is if the tower wasn't in the richest neighborhood of London, the council wouldn't give a shit about its insulation and energy savings. And my guess is they added these reasons to make themselves look benevolent instead of saying "We're adding cladding because the tower looks shit otherwise."
Actually, one of the reasons for the beautification is that it was quite close to some expensive real estate.
Oh, actually we're agreeing. I read your comment wrong.
This seems backward to me - why do you think a council with more financial pressure care less about their bottom line, and a council with less financial pressure care more?
At least, that's what I would expect here in the USA.
It doesn't make much material difference, but I think it was more to do with insulation and saving energy, rather than aesthetics.