After all no one would consider using high reverse thrust when taxiing - for all the obvious reasons, yet we accept full reverse at 30 knots ground speed during landing if landing into a 30 knot headwind (60 knot IAS v 30 knot ground speed)
I would also suggest that the risk of FOD from ingesting debris kicked up by the reversers is considerably greater at 30 kts in still air than at 30 kts GS into a 30 kt headwind i.e. 60 kts IAS - hence the IAS limitation.