Disagreements over where a boundary runs can outlast the governments that inherited them. The slow pace comes from the nature of the evidence and the politics of accepting any answer.
The documents were not written for this
Many boundaries were described in treaties drafted long ago, using landmarks, watercourses and phrasing that made sense to the drafters and to nobody since.
Rivers move, named features fall out of use, and the maps annexed to old agreements were drawn at scales too coarse to settle a modern dispute.
Each side can therefore argue in good faith from the same text and reach different lines on the ground.
Ground truth and legal title diverge
Boundary law weighs the written title heavily, but it also considers how territory has actually been administered over long periods.
Where one state has policed, taxed and governed an area for generations, that conduct becomes evidence, and the other side's paper claim weakens.
Assembling that record means gathering decades of administrative material, which is slow work and often incomplete on one side.
Resources raise the stakes
A line through empty terrain matters little until something valuable is found near it, and maritime boundaries carry rights over the seabed and fisheries.
Once economic value attaches, the cost of conceding rises for both governments and the incentive to keep negotiating quietly falls away.
Disputes that were dormant for generations frequently reactivate at exactly the moment survey results are published.
Domestic politics constrains the negotiators
Territory is treated as indivisible in public discourse in a way that trade or tax policy is not, so any compromise is easily framed as surrender.
A negotiator who concedes even an uninhabited stretch may be unable to carry the agreement at home, which caps what can be offered privately.
Governments consequently prefer an unresolved dispute that is calm to a settlement that would be politically costly to sign.
Why third-party settlement is used sparingly
International courts and tribunals can rule on boundaries, but only where both states agree to submit the question.
That agreement is itself a concession, because it means accepting a result neither side can predict, and it is often the hardest step in the process.
When it happens, the ruling ends the legal question quickly, which is why the negotiation about whether to arbitrate can take longer than the arbitration.