Sadio Mane earns £150,000 a week (and that's not including any performance-based bonuses and sponsorships) so he could buy a couple of Ferraris every month if he wanted, but there's only so much money someone needs before it becomes unnecessary and it's nice to see people actually do something good with their money rather than just blow it all on overpriced clothes and cars. I'm surprised more players don't do it really as nobody needs the amount of money they earn. I wouldn't even know what to do with 150k a week. £150k a year would make you a very wealthy person in the UK and you'd be in the top 1% on that alone.
To expand on that, there's only so much money can buy to make a person happy. Once you get to that cliche status of "the man who have everything" it's even possible that being able to buy anything you want will cause an existential crisis if you can't find something to make life more fulfilling.
I'm glad that in his search for fulfillment, he found something that also benefit others.