I believe they are required as part of FAA regulations to ensure that no manned craft are within 15 miles of the landing zone? Something like that, at least, which would complicate a tether-based approach.
I think the suggestion was a separate but tethered unmanned platform, which would presumably have less vibrations. I would imagine it's just not cost-efficient for SpaceX, as they'll be able to recover the footage later regardless.
Who needs a tether? Ubiquiti makes gear capable of slinging 400+ Mbps over 25km in a straight line. For about $1500 they should be able to shove the "last mile" to a ship outside of the exclusion zone and put the sat uplink on the ship.
They have grid antennas with a slightly wider beam, or maybe a sector style with 20-30 degrees could be used. I just think it's easier to engineer a workable ship-to-ship stabilized radio solution rather than deal with the ship-to-sat dish which probably has much tighter tolerances.
