No logic in buying a ticket for just 1 satoshi? I don't see much of logic in keeping 1 satoshi either.

It won't be a lot of money even if BTC hits $1 million, right? So, I wouldn't call it "spending money", if you ask me. It's spending 1 satoshi and making your life a little bit more entertaining with that.

It's worth noting that any user of the freebitcoin site can easily get a few thousand tickets and sats with the daily free spins of the wheel of fortune. So there is no particular need to spend sats to buy additional tickets. As for me, if a user has some sats left on his balance, it's better to spend them on buying FUN tokens rather than lottery tickets.
I absolutely agree with you, but believe it or not, if your getting lottery tickets from free rolls is disabled, and you have just 2 WoF spins per day on average, there are some weeks when you have zero lottery tickets. I personally consider those weeks lucky ones because I prefer getting RPs or some satoshis from my WoF spins, but in that case I buy at least 1 ticket to make my chance winning the lottery not zero.