ADS-B Exchange used to have another incentive to feed in the form of free API access, subject to certain limits and for noncommercial use only. They stopped that a year or two ago, I believe because various commercial operations kept abusing it.
EDIT: In their FAQ it currently states: "In very limited situations ADSBexchange.com may choose to allow non-profit, research, or educational entities access to the historical data or API at reduced fee, in these situations such entities must meet all other requirements including hosting a feeder. ADSBexchange.com API pricing is a fraction of the cost of ADS-B data available anywhere else." To me that is quite different than their previous policy of providing automatic noncommercial API access to anyone hosting a feeder. It removes an incentive to feed and discourages use of the API.