Why is 6.8 SPC still a thing when 6.5 Grendel is more and more popular?

[stanc]

I fought the 6.8 SPC tooth and nail back when it was being proposed as the Next Great Military Cartridge because its "performance" was based upon false promises (2800 fps for a 115gr SMK from a 16" bbl) and juiced testing (explosive performance in gel testing using tweaked varmint bullets)...

For example, the Tri-Service Working Group (TSWG) that was testing 68SPC and 65G vs. 556, etc., insisted that Alexander Arms submit Wolf 6.5 Grendel 123gr soft-point lead-nose bullets...

I never cared what civvies shoot, and still don't.

Ditto. I disregarded the testing of hollow point and soft point loads. Like you, my interest was military utility, so I compared full metal jacket.
Even at realistic velocities, 6.8 SPC 115gr FMJ gave superior terminal performance, producing much earlier yaw than 6.5 Grendel 120gr FMJ.

Today, trying to decide between the two cartridges, I don't understand why someone wouldn't choose the 6.5 Grendel...

I can think of a few reasons:

Optimized 30-rd P-Mags

Disintegrating Links

Machine Guns
[video=youtube;z2Pq4_XdA-k]https://www.youtube.com/watch?v=z2Pq4_XdA-k[/video]
https://www.youtube.com/watch?v=z2Pq4_XdA-k