Because, insofar as I've been able to ascertain in a few hours of experimentation, the 4DOF-supplied .22LR drag curves don't come close to matching observed data.
Yeah yeah I know... garbage in garbage out. I use an indoor range - level, precise range measurement, zero crosswind - to set my zero, and I use a caliper to measure impact distances from POA - Hornady emphasizes the necessity of getting these right. But here's the thing that I'm still waiting to hear from Hornady about: why do they get different drag curves for Lapua Center-X, Lapua Midas+, and SK Standard+ at a given velocity when all three use the same bullet?
Because of the way 4DOF works, truing of their supplied curves to match observed data is extremely limited (via axial form factor). I've watched the Hornady podcasts that get fairly deep into setting up the app, and their contention is that correct inputs will yield correct outputs and truing isn't needed.
Well, I am slowly gaining confidence in the app with centerfire bullets in their library, but I have absolutely no confidence at all in their supplied .22LR curves. I only know one other person who uses 4DOF for .22LR, and he doesn't use their curves either.
The only way I've been able to make 4DOF match observed data with .22LR is via the BC calculator.