...and it can be a welcome bonus or just a random bonus sent to users to increase their engagement, but it's not a bug just a strategy.

While reedeming most users don't give attention to all the details that is why the confusion with no deposit with no wagering but later found about the wagering requirements that's hard to complete or not really worth the rewards but it is what it is, we just need to be careful when going after the free money.
This is clearly a Bc.game strategy, even I myself almost every month receive email messages about various bonus codes, maybe you are right, this is just for user engagement to keep playing at this casino.
Completing the wagering requirements is indeed unreasonable to pursue, just for fun with the bonus balance.
Need to pay attention in bc.game there is a deposit balance and bonus balance, then the redeemed code will go into the bonus balance, even I don't see someone who managed to achieve this.
I doubt that it's possible for anyone to achieve that wager requirements, although I have tried up to three times when bc game credited me with the bonus but for all those three times it felt like a journey of no ending so what I do is just use it to keep myself active and busy by trying out possible games that might seem interesting enough to later funds some real cash so I can replicate the winning experience I had but if the case turns different I just let go. I think I go the bc.game email four days back and I will still try it out again who knows I might be the lucky one to reach the requirement.