A player will feel more comfortable playing with bonuses if the bonus system isn’t tied to their main deposit. This week, I’ve already managed to wager through two 5 USDC bonuses with a 35x wagering requirement (but that was at a different casino). I didn’t have to cancel the bonus or worry about losing any of my deposited funds. It was just a bonus from the casino, so bonus systems can be completely different from one casino to another.
You have said it all here mate, because this is a perfect example on how a bonus from a casino should look like, because once the bonus system is being tied to your main balance, you will be afraid to initiate any bonus offers, because you cannot just back out without losing your main deposit in the process, or being punished. So if the bonus is independent as it should be, many gamblers will want to give it a try, than when it's tied to your main balance.
With my experience with bonuses in most casino's, I no longer see bonus as something interesting because it's more of a trap to make you lose your deposit, due to the unrealistic wagering conditions they always comes with, that's why I would rather gamble on my own terms, with my money deposited, and move on from that once am done.