Probably for the same reason that we have been reading on this forum that people are having trouble with 55 grain Sierra Blitzkings and 55 grain Nosler Ballistic Tips not shooting well in 1 in 14 inch twist barrels.
The boat tail makes a bullet longer. The 55 grain versions are long enough already to have problems stabilizing in some barrels.
When dealing with plastic tipped bullets, I have never found any of 55 grain versions to shoot well in my three 22-250's except for the Hornady.
I used to shoot a lot of Sierra 55 grain spitzer boat tail bullets, but they were lead tipped and were a good deal shorter than the new plastic tipped bullets. They worked well in a number of 22 caliber rifles.
Strange, I am not challenging the statement that some are having problems shooting the 55 grain Plastic tip boattails in their 14" twist barrels, but I have 5 22 centerfire varminters, starting at 222 and ending at 220 Swift. All are 1 in 14" barrels, and they all shoot the 55 Ballistic tips superbly. Have not tried the Sierra offering, but will see soon. Guess it may depend on an individual barrel. Regards, Eagleye.
