It seems that independents/moderates have platforms that are a mixture of surprisingly liberal along with surprisingly conservative views.
They are catered to by the democrats with candidates that offer policies that don't particularly fix anything but make you feel like they are supposed to. "Like you, I think it's terrible that college tuition is skyrocketing year after year. To fix that, I propose a federal savings vehicle that will let families save up to $200, tax free, in order to help mitigate that costs. I believe EVERYONE deserves a chance to go to college."
But realistically if you want to get pegged as a moderate you need to just be publicly idiosyncratic about one thing across policy lines. Justin Amash is very conservative, but extends that through positions that put him at odds with his party on foreign policy and it lends him tremendous credibility.
All that centrist dems offer is "Hey, don't worry, I won't do that much, so please don't blame me if the party does something you don't like".