What the title says - the Glaive's heavy attack, the explosion, is (still) unable to crit. The throw can crit, but it's not actually a heavy attack, so it doesn't benefit from the 2x crit chance from rivens and True/ Sacrificial Steel. This is true for all Glaives and even the Wolf Sledge.   This has been the case since sometime December last year, and it significantly weakens the Glaive part of Glaive weapons.