The most likely reason for the service being discontinued is the expiration of an agreement between SEA TOW and MARITEL. On September 25, 2020, MARITEL filed a federal lawsuit, described as follows:
Bass, Berry & Sims filed a lawsuit Friday in Tennessee Eastern District Court on behalf of MariTEL Inc., a radio communication services business, and its affiliates. The complaint accuses Sea Tow Services International Inc. of continuing to use the plaintiff's licensed spectrum for transmission after the expiration of nine-year agreement. Counsel have not yet appeared for the defendant. The case is 3:20-cv-00424, Maritel, Inc. et al v. Sea Tow Services International, Inc.
Apparently after that action, SEA TOW decided to discontinue its automated radio check service.
Regarding VHF Marine Band channels 24 to 28, the frequencies were used for many decades to provide ship-to-shore public correspondence, that is, to provide a link between VHF Marine Band ship stations and the public telephone system network. MariTEL was the licensee of many shore station transmit facilities that were used to provide the service, referred to as VHF Public Coastal Service Areas. MariTEL was the licensee in VPCSA 1 to 9. With the arrival of cellular telephone communication coverage across the entire United States and its coastal waters, the use of ship-to-shore linkage to the the public telephone system network dramatically decreased, and MariTEL's license to use those frequencies and to provide those services was thus significantly reduced in value as a source of generating revenue from a commercial operation.
Based on the limited information about the lawsuit, it is reasonable to assume that SEA TOW and MariTEL entered into an agreement which permitted SEA TOW to install and operate their own automated receiver-transmitter services on channels 24 to 28 at various locations. The use of the SEA TOW service was at no charge to mariners, but the automated radio checks usually included a promotional announcement about the availability of towing services.
SEA TOW's use of Channels 24 to 28 under their agreement with MariTEL was providing a useful public service. The discontinuation of that service removes a useful public service from the VHF Marine Band. I am not aware of any plans for a new use of those frequencies by MariTEL. I suspect that MariTEL wants to retain their license to use those frequencies in order to receive some compensation from the FCC by ultimately agreeing to return the frequencies back to the FCC to be licensed to other services. The FCC has exhibited a generous policy of compensating spectrum licensees who must surrender allocated frequencies and move their services to new frequencies.