This might be true, but it's also misleading. Intellij is a pretty huge application, with a gigantic set of features and capabilities, likely far more substantial than even the largest/most complex Electron app out there.

Intellij would require notable memory and cpu regardless of whether or not it was Java. See XCode and Visual Studio for comparison, as they are probably closer to the same feature profile than something like VSCode would be. Their memory footprint and performance is not what I'd call substantially better than Intellij (and as with most comparisons of this nature, many caveats exist around which plugins/addons/features are in use).

Would Intellij have a better resource profile if it were native? Ya, possibly, but it's also possible that another language/platform would have been a significant barrier to long-term success. Not many cross-platform UI toolkits from 2000 to choose from, and many fewer have continued to be well-maintained and usable today.