Real money rewards bring new players to bingo sites with no initial risk. The reason is that new players are often hesitant to deposit money is they aren't sure which site is the best for them.
No deposit offers allow new players to try a site without an investment.
Not having an initial deposit allows players to preview games and see what the site can offer.
Some players earn enough through their no deposit offer that they earn small payouts. This makes players likely to come back and make a deposit.
No deposit bingo offers benefit the new player and the site alike, as new players are likely to find that the site offers them the games and payout opportunities they are in search of.