I think the point is the politicians are the ones implementing it, irrespective of their drafting skill. It's not just about the wording of the agreement, it's

I think the point is the politicians are the ones implementing it, irrespective of their drafting skill. It's not just about the wording of the agreement, it's about their understanding of the others' position and which bits they might actually give way on, about how much they and fellow politicians that might replace them are willing to lose, about which pledges they expect to see broken/break and the expected consequences of breaking them, if any. Frankly the fairest settlement of all time which one of the parties immediately breaks at great cost to the other is less likely to work than a horrendously skewed agreement that gives some much needed wiggle room. Even if the winning open heart surgery plan was drawn up by a couple of brilliant surgeons, I'd still expect the person wielding the tools to prefer their own plan, and probably for the best