The build date does only make sense for custom/self-compiled bitcoin-core versions because we are using static build-dates for our deterministic release builds.
Having a quick option to get the current datadir is much more valuable for debug purposes.
I could optional re-add the build-date for self compiled versions if someone brings up a concrete reason/value to keep it.
Optional this could be extended to open the datadir in the OS file explore when someone clicks on the label (Would require some platform dependent code: http://stackoverflow.com/questions/3490336/how-to-reveal-in-finder-or-show-in-explorer-with-qt).