Where there's a whole lot of poor customers, there's people who can get rich by servicing them. Even if it's not very much profit per transaction (dependent on philanthropic or gouging tendencies), it's a lot of transactions1
. And with a large potential base, there's room for many low-scale entrepreneurs, a lot of mid-scale ones and several high-scale ones all jockeying to do more (likely also enriching others, from top staff to corrupt officials, as they go) and accumulating significant wealth in the process. Maybe sparking a dynasty tbat kick-starts other family members into hyper-entrepreneurship.
(Even in Slumdog Millionaire, that Million has to be a practical amount of prize money, actually available to be shelled out by the production company, and that sort of wealth is available (over time, if not in a single paypacket) to pay TV execs, Bollywood actors, and certainly the people building (and taking sky-high rents from) the posh high-rise real-estate that famously directly abutts the slums quarters (or the slums abutt the posh district, give or take whatever security measures are taken).
India has children scavenging rubbish dumps and
a Mars-capable national space-programme (the government also takes "a lot of little payments", when it can). That's the kind of contrast we have on the sub-continent.1
My theme of the day seems to be "a lot of little things added together".