I don't approve of macroing either. Regardless, I wouldn't say WK is "impossible" to macro without knowing exactly what people would try to use to achieve it, but I think there are enough variables in it beyond just running in a set pattern talking to non-moving NPCs to make it rather impractical to try to macro, plus you would need 3 toons for an effective farm of the whole map.
On that note I believe SSG's (or previously Turbine's) stand on macroing is they're ok with a macro set to some repetitive tasks such as item exchanges and perhaps random loot crunching, but someone should actually be at the keyboard if a GM drops by to check the automation. This basically makes the old cruci entrance macroing while you were working/sleeping a complete violation. To prevent similar cases that they are otherwise unable to police all of those optionals have been set to no longer grant XP.
The most probable answer would be that SSG have no "fix" the optional and little to no additional resources that can dedicate for a long term fix (for now) for the decay issue, and also do not have the resources to police opt farming. They're also not keen to blanket nerf optionals to keep some incentives for players to sidetrack in quests. Was that the full intention of the devs? Maybe not. Is it an explicitly bannable exploit/offense at this point? I doubt it.
I do try to avoid farming WK excessively especially when on builds that can handle content fine, but it's a reality that not everyone can easily find XP otherwise, and many quests are only "efficient" after you add RXP into the equation and if your current build/stacked toon can faceroll the quests. Druid's Curse and High Road for example are still relatively miserable XP even with BB active, and can easily turn ugly for an ill-prepared player or group. If WK was nerfed hard enough to be not worth the time running these people will likely just revert to running daily chains like VoN3/4, Spies, etc. People still do those now if they don't have sands or don't want to burn WK. They're not going to spend an extra hour or half per quest they cannot realistically handle efficiently.