In the case of WRNN, Verizon has a bit of a deal going on with them. They run their FiOS1 news operation out of WRNN. Perhaps carriage of RNN's subchannels is somehow tied in with that.
In the case of a must carry station, the station that elects must carry status is only entitled to force its primary signal onto cable.
In the case of a retransmission consent station, the sub-channels are up for negotiation. Antenna TV is owned by Tribune (which owns WPIX). It's safe to assume that carriage of Antenna TV was negotiated. THIS TV, on the other hand, is also a WPIX subchannel and does not enjoy the carriage that Antenna TV does. THIS TV is owned by Weigel Broadcasting and likely leases its channel from WPIX and isn't covered by the WPIX deal.
Doesn't Tribune own WTIC-TV? If so, then likely the same deal applies with getting Antenna on to your cable lineup. WTIC-TV, as a Fox network affiliate would generally fall into the retransmission consent category.