This psychological tactic works more often than not. Personally, I get tempted whenever I see wheels spinning or whenever I receive scratch cards with hidden rewards even though I know deep down that I probably will earn an insignificant amount.
This is why I usually try and avoid such stuff whenever possible in order to resist the temptations. Sadly, most gamblers cannot resist fall prey to such temptations.
Most of them don't realise that such games usually have the highest house edge when compared to games like Dice, Baccarat etc.
Of course it's all about psychology, but the important difference here is that Freebitcoin is provably fair. So yes, you do know that your chances are really low, but it's free. Better than any paid lottery out there IMO. And it takes only a few clicks to get the result. I've already won 5000 satoshi 2 or 3 times (which is $7 or more by the way).
Obviously speaking you can make it work if you keep on grinding for free, after all freebitcoin would give free...bitcoin?
That is why it makes sense for them to make it work for free. However we have to realize that there are people who lose money as well, you can deposit money and gamble with it. So, provably fairness comes into play there, if I had just free money I would end up with not a provably fair place?
I would not really care too much, since it was free, I played something free and got scammed for something free, not that many people would actually care about it. However if it is paid, there are tons of people who gamble and lose money here, at that point it had to be provably fair and when you look at it freebitcoin has used the same logical and technical awesome provably fair system and everyone agrees that it is fair and nobody found anything otherwise.