I couldn't agree more tbh and whilst you might be right, sometimes we cling on to things that remind us who we are, what we have and that we are indeed human after all.
Whilst its partially like RIP threads in GD, where everyone HAS to say something about how sad it is that some random person they've never met has died, in large part I think because people consciously or unconsciously want to look "good", as in nice, kind and doing what everyone else does.
Muamba gets around a bit, he's played with so many players already, and you get the very genuine impression from a LOT of players that they know and deeply respect him. While on the outside "smart" footballers are looked down on, I wouldn't be surprised if many within the sport greatly respect those who didn't pee their education away, especially older players. Likewise Muamba wasn't gifted his life, he had a bad start to life, escaped, and everyone says has worked exceptionally hard, worked hard to achieve well at school while training hard in football which many other players(maybe most) all but ignore school while getting into football.
He seems to work hard, still likes to learn, isn't someone who goes around banging hookers/getting smashed, he's simply well known amongst players playing in England and Europe as many European players would have come across him at international competitions.
You can go out on the pitch and try and kick everyone, cheat, foul and injure and gain hate amongst players of other teams, and there are those players that players at all clubs respect greatly.
Basically in this case I think its genuine, you'll have players at Barca and Real who have either played with him, trained daily like Cesc, or those who played against him in international competition, or those at those clubs who simply feel badly for players who knew him.
I mean this stuff does happen to a lot of people, its not surprising the biggest reactions end up being for people everyone unanimously agree is a genuinely really nice guy in football.