i don't think of the rock superstar groups embracing funk and disco as an act of bravery or cowardice
it was just them doing what they always did, which is take a passionate interest in black music
Rod Stewart, The Stones, et al, were into the blues and soul and R&B in the Sixties. And - hardly surprising - they remain interested in what black music comes up with in the Seventies - funk, disco, also reggae
So Jeff Beck (in Beck Bogert Appice) covers "Superstitition"
Foghat - who used to be Brit-blues band Savoy Brown i believe - have a really nifty slap-bass bit in "Slow Ride"
Eric Clapton covers "I Shot the Sheriff"
Stones become really enamored of Pete Tosh and put out one of his records on their label.
Led Zep do James Brown-like and reggae-ish things on Houses of the Holy (the admittedly horrid "D'Yer Maker" complete with music-hall joke title)
And all of that is pre-punk and pre-disco proper.
So it's that typical British orientation towards black music
But also they're musicians, they hear something new and cool - Larry Graham's bass style, Chic-y rhythm guitar- and they want to have a go
The other contributory factors would be:
they are leading typical superstar glitzy lives, which would mean actually being in discotheques like Studio 54, hearing this stuff, digging it (helped by the white powder no doubt)
they do like to have hit records, be on the radio, and these sounds are the sounds that are selling. BUt probably it's more about wanting to still be in the current musical conversation and maintaining their profile, than actually mercenary, since they could coin it just doing the same old thing to their massive fanbases.
I suppose you could say it's a little brave in terms of their existing audience - Queen doing an overtly discofunk (and Chic-resembling) tune with 'another one bites the dust', Steve Hillage basically doing funk-prog in the late 70s - but really i would say it's just business as usual: Brits and the love of black music. An organic thing, rather than like with postpunk where it's more gestural, more of a stance, and also being less proficient musicians, the postpunks come up with this mangled quasi-funk sound that is probably more interesting ultimately (as much as i love e.g. "Miss You" or indeed "Another One Bites the dust")