Guess you are talking about cloud to ground lightning which is not in DCS, cloud to cloud lightning flashing on the cloud base and reflecting on the ground etc is very realistic as not all lightning hits the ground. Weaker or dying storms can produce a lot of cloud to cloud lightning, there's many variables why.
But yes I agree though there also needs to be cloud to ground lightning bolts to mix things up and make storms look more realistic and exciting to fly in, it's one of my favorite conditions to fly in Flight Sims for me as it's more challenging and looks cool (one of the reasons I love chasing and photographing storms when I can)
Hopefully something in a future build!