Why is it that the consensus for these two blackjack variants calls for massive bet spreads?

I understand that 8D blackjack games for example, typically require a larger spread of at least 1-16+ when taking a play-all approach to overcome the increase of negative expectation hands. But I've read in various places that 8D SP21 requires a spread of at LEAST 1-20+, sometimes even as high as 1-40, when using play-all to pull a reasonable profit. Its SD is slightly lower than traditional blackjack too. Wouldnt its various bonus multi-card payouts somewhat negate initially negative expectation hands somewhat too? You're more likely to pull 2-6 and hit 19-21, as is the dealer, but they're not getting paid out 3:2, 2:1 or 3:1. Plus you have the advantage of being instantly paid out when you do. Surely this must offset the need for using a huge spread somehow?

Anyway, I brought this up for my specific case. I'm using a wong out point of -1.5/-2 TC on 8D H17 Pontoon. The HE is .40%. Whereas blackjack is around .58%. Why would I need to use a 1-16 bet spread even when I'm wonging out of most negative shoes? Obviously the return of using higher spreads with wong out increases profitability dramatically, but my BR isnt overly large currently and I need to balance EV with my calculated RoR. Surely using either a 1-10 spread, or 1-12 spread would suffice when wonging out at -2 TC in this case?