Charging abroad: why are roaming fees still so random?

Just got back from a road trip through France, Belgium, and the Netherlands. Honestly, the charging networks themselves were fine, but the prices were all over the place. Same car, same battery state, but I paid anywhere from €0.39/kWh to €0.79/kWh depending on which app I happened to have on my phone. I thought the EU roaming regulations were supposed to fix this? Or does that only apply to mobile data? Has anyone found a reliable way to compare charging prices across networks without installing ten different apps? I know about the big aggregators, but they never seem to have the live rates right. What's your strategy for avoiding getting stung on price when you're outside your home country?