There is a good reason for this. If you raise the platform too high, you run the risk of getting the tip of your board under the platform, which can be dangerous.
Obviously everyone is going to run a different weight setup, which will change the height of the platform and how high it can or should be raised, this would either lead to
1) The manufacturer making one in safe tolerances, that will probably not do a whole lot of good,
2) The manufacturer making one very adjustable, someone getting the bottom of the board stuck under the platform, face planting into the transom, getting hurt and suing.
Now what they SHOULD all be doing is make swim platforms that are shaped and sized to not interfere with the wake from the side of the boat AND making the bottom of them flat and smooth aka no lip on the bottom of the platform.
We have tackled this problem on the Supra with great results as shown in this thread,