If you understand the reason that a standard lock can be shimmed, you will realise that access to the rear of the lock is necessary. This involves the tail-piece to be removed and a shim to be introduced between the pins, at the shear line.
The tubular lock uses a different construction...
The shear line is perpendicular to the plug and is shrouded by the cylinder housing. There is no way that a shim can be inserted...
Tubular locks can be manually-picked quite easily though.
