A lot of buried carbon is digested by anaerobic bacteria, which produce Methane (also a greenhouse gas), so there's that.
It’s too dirty to put in the natural gas grid.
I looked up the numbers, in the US, it’s something like 70% burn on-site for electricity, 20% burn in some nearby use (e.g. process steam or greenhouse warming) and 10% was cleaned up enough to pipe into the natural gas grid.
That’s by facility count, not BTUs.