Confusion about TVS-wiring with RS-485
The TVS between each line to ground limits how far away each line can get away from ground (it clamps the common mode voltage). The TVS between the lines prevents the lines from getting too far away from each other (it clamps the differential voltage).

In a way, the TVS from each line to ground does indirectly prevent each line from getting too far away from each other. But if the common mode limit of the lines is larger than the differential limit, then TVS diodes which are sized to limit the line to ground difference won't protect against exceeding the differential limit.