Nexstar Broadcasting owns WPRI, Providence, and carries Antenna TV and Rewind TV on two of the WPRI subchannels, so they have a particular advantage being aired there.
In Boston it seems to depend upon the many, often-changing, financial deals between the group owners. WVCC-LD was purchased relatively recently by Bridge News, owner of NewsNet, and has made some signal improvements. Perhaps Antenna TV could return there at some point? Also there is the planned transmitter mover by WMFP / WWDP from ch 10 in southeast MA to ch 36 in Needham, which could eventually result in some subchannel shuffling.