For personal events, like a divorce or funeral etc, they might help because they care about another person, and it's not about getting anything in return. They might see a family lost everything on the news and want to help them, or read about someone with an illness who needs help for treatment or bills etc, many different circumstances.

For business, usually for those seeking the funds for some business endeavor, they will often set some sort of terms and the investor gets a certain perk like first access to the product once it is built? if they help to donate etc also many ppl might come up with a cool idea that others like but not have the funds to get it off the ground and if enough people like the idea and want to see the idea come to full realization then they can contribute to making that happen. In this circumstance with the home, i think people who are getting married or having some other celebration might instead of asking for gifts from loved ones, ask them to fund their home downpayment via this method, many couples already do this with asking guests to their events to rather than give a gift, give them $ for a honeymoon or something etc. :)