Brokers who decide not to syndicate do so, generally, because they don’t like the way outside websites handle their listing data. Some websites only display certain parts of the listing information, or the listings they display aren’t updated often enough – sometimes appearing available when they’re actually off-market. Some websites don’t openly display the listing broker or agent’s name or contact information.
There are a variety of reasons some brokers choose not to syndicate, but the bottom line is almost always related to how their data is handled once it’s shared beyond the MLS. At the end of the day, it is entirely the broker’s choice and you have to weigh the pros and cons to make the decision you feel is best for your business.