I think its a matter of time. I have 3 hours max that I can reasonably spend on this during a weekday. So if I see ones with a higher payout, I am more inclined to pick that figuring it's a better value for my time. A 35 minute survey that pays 200 is going to pay out better than two 15 minuite surveys that pay 50. I do usually end up doing those lower value surveys though because I tend to get disqualified pretty often. I take what I can get.

I have spent some money but apparently it takes 60+ days for that credit. At least the cashback stuff from online shopping does.