The end screen of the Three Stooges game for NES....
The plot of the game is that the Stooges had to earn $5000 through various jobs to keep the orphange from being torn down. Thus, in this case, they've generated a cool $15,165 in profit. It's a tidy sum, sure, but laughably insufficient to fund three marriages. Nowadays, fifteen grand won't even cover a single wedding. I suppose to cut costs, the weddings could just take place at City Hall. I know the cliche is that every girl dreams of her special wedding day (this was Monica's storyline for the entire sixth and seventh season of Friends), but in this case, I doubt the brides will complain too much. They're marrying the Three Stooges, for god's sake, so they're clearly not picky.
Onto motive. The orphanage owner/mother is a curious psychological profile. On the one hand, she is obviously grateful that the Stooges have saved her orphanage. She is surely impressed with the valour of these three young (?) men. She also has three single, attractive (?) daughters. Her thought process here was similar to that of the man who first invented the banana milkshake.
Cut to a man holding a vanilla milkshake in one hand and a banana in the other. He looks at the banana. He looks at the milkshake. He looks back at the banana. He looks back at the milkshake. He looks back at the banana. He stares at the banana. He looks once again at the milkshake.
Man: Hey, wait a second....
The game is apparently set in days of yore, when parents were free to set their children up into arranged marriages without any concern to their feelings. The $15,165 in this case is something of a dowry. The girls all look pleased, as shown by their hot and heavy makeout session, but reality will soon set in. Can you imagine how awful it would be to be married to one of the three Stooges? You'd never get a moment's privacy. The other two would around 24-7, causing mischief, breaking up intimate moments with pie fights. The sex would probably be lousy, given that all three Stooges have taken enough junkshots in their lifetime to ruin their organs.
In summation, if your orphanage is saved thanks to a fundraising effort from three goofy bastards, don't pimp your daughters to them.