Killers, depending on the circumstances may use whatever murder tools and disposal mechods available more often if the murders aren't planned, imo. Killers who intend to kill from the get-go use murder tools and disposal methods of choice, usually what fulfills their sick fantasies and/or what they feel most comfortable using. Though, burlap is fairly easy to come by, some of us on websleuths didn't know that, and together we represent community statistics. How many serial killers would think of and use burlap bags? Generally, if a murderer disposes of victims via bags, it is most often plastic garbage bags. But, not LISK. I think whomever murdered the GB4 was familiar with burlap bags prior to the murders, regardless of how easy it might be to obtain said burlap. MOO.
I am familiar with LI and lived there for a number of years until recently. I would buy horse grain packaged in burlap. Nurseries, upholsterers, and others use burlap. Overall, the use of burlap bags seemed relatively limited on LI, however. Therefor the choice for LISK to use burlap? This stands out to me like like a stop sign.