This is really about breech support.
The bigger tenon puts more barrel steel around the chamber.
A coned breech extends breech support.
Larger cartridges require larger area of chamber, so it's appropriate to increase chamber support for this.
Otherwise the chamber expands more (due to it's area), causing more brass yielding (upsizing), potentially leading to difficult extraction and opening primer pockets.
That's neither gorilla, nor Hollywood. It's for real.