Could also be because they don’t exactly have full network service. Like their CBS is a special feed of WSEE in Erie, PA with alternate programming in place of Erie local programming, their NBC is just a simulcast of WNBC via WKAQ-D3, their ABC is just a near-simulcast of WABC via WORA-D1, and their Fox is locally owned WSJP-L2. They likely just can’t come to a streaming deal with their respective networks, especially probably the Fox station, or their contractual agreements with the networks only allow streaming to the mainland US and not also PR & VI.
Heck, entering a PR ZIP code on the YTTV website just tells you straight up it’s not available!