I sympathise with the OP - many airlines like to cultivate goodwill with their frequent fliers and extend exit row/preferred seating privileges to them and I don't think it would hurt EK at all to do that by having an automatic system in place to allow seat selection of preferred seats. As one of these frequent fliers, I wouldn't complain if this system was in place (although I prefer adjacent seat blocking on a totally personal note).

However, I also see it from EKs point of view: I don't think they want to take too good care of their frequent fliers as they don't want to fall into a trap of excessively catering to them and go on a path of US airline style loyalty programs. They must have some analysis showing them that x% of gold/plat are either captive or have no authority to make travel plans or are price sensitive enough that the incremental revenue from their loyalty doesn't make that much of a difference to their operations.

So when it comes to seating, why bother putting this thing in (with additional cost and knock on when you have to rearrange people denying them a "published benefit") when it's unclear whether there's any real upside at all. Frequent fliers are still flying with them without this so why give them free stuff for goodwill when it's not entirely clear that that goodwill has enough of a reciprocal benefit to their profits?