Likely because they have hoards of the old batch of JSB.
More so because they're not shooting the JSB pellet with the most problems: the .22 Monster RD in those sub20 and sub12fpe field Target disciplines.
Pretty trendy right now to say JSB quality has gone down, but that's painting with a pretty broad brush when considering how many varieties they offer and how few of those varieties have issues.
The .22 Monster RD has certainly suffered from flyers, more so in later years than when it was introduced.
The .22/18.13 is hit or miss, but has been for a long time, good tin, bad tin.
The OTHER JSB variants that I enjoy in large quantities don't have those flyer problems. Those would be the....
.22/13.43
.22/14.3
.22/15.89
.20/13.73
.20/15.89
.177/7.87
.177/8.44
.177/10.34
And alot of those have been recent purchases, not old stock.
As I initially said in this topic, AAFTA and WFTF guys are shooting almost entirely JSB. Yes, random non-JSB shooters here and there, but the other 98% are sticking with what wins.
The shift to non-JSB is because those other companies now have better BCs in the big heavy stuff (mostly .30). And we hear about that a lot from the shooters of those long range product showcase/exhibition matches (EBR/RMAC/PA Cup).