Well, that's a reasonable reason and at least we don't wonder anymore. Are you inactive in the last few weeks? so we can assume that it is their way to bring you to be active again, similar to the promotion offered by other casino.
I haven't made deposits on Shuffle for a long while. My last deposit was two months ago. My PnL statistic is also negative there. So, my inactivity could be the reason for the exclusive bonus.
weekly bonus is also very low less than $ 0.1 this means that Shuffle really does not apply the basic bonus to the VIP level it's pure based on house edge.
Only one or two casinos have the base reward system for the weekly and monthly bonuses. Otherwise, all casino bonus system is same as Shuffle. You have to keep wagering to get the bonus always.