As an aside, when i top up my prepaid mobile i have the option to donate the top-up to another number. Yet dating sites i've seen don't allow subscribing someon

As an aside, when i top up my prepaid mobile i have the option to donate the top-up to another number. Yet dating sites i've seen don't allow subscribing someone else for a limited time (by opting-in on their side of course). Is there some reason as to why this is not an option on most dating sites? Seems courteous, but it might lead to scams or begging perhaps?