The CEAC as implemented in DAMPACK calculates the probability an intervention is preferred (or considered optimal), not the probability the intervention is cost-effective. Multiple interventions can be cost-effective (not dominated and ICER<WTP) but only one can be preferred (maximize NMB or NHB, or equivalently, have the largest ICER below WTP threshold).
The CEAC as implemented in DAMPACK calculates the probability an intervention is preferred (or considered optimal), not the probability the intervention is cost-effective. Multiple interventions can be cost-effective (not dominated and ICER<WTP) but only one can be preferred (maximize NMB or NHB, or equivalently, have the largest ICER below WTP threshold).
Here is an example of a CEAC where the Y axis is appropriately called "Probability cost-effective". Note that unlike the DAMPACK implementation, the sum of the probability each strategy is cost-effective at any given sums to a number greater than one, particularly for larger willingness-to-pay thresholids. https://www.researchgate.net/publication/306025962/figure/fig2/AS:393531618283544@1470836657983/Cost-effectiveness-acceptability-curves.png
I suggest changing the Y axis in the DAMPACK ceac plot to "Pr Preferred" or "Pr Most Cost-Effective"