So are saying that they have chosen to support other software developers but not quicken?
Betterment won't pay Quicken the fee Quicken wants to be included in their downloads. That is what Betterment support told me. Banks supported by Quicken don't get to be in that list for free. Betterment is totally open to Quicken downloads though. Many other services support Betterment, as noted in the OP. It is just one way Betterment keeps fees down.