 This is because of (a) surface tension at the interface between quark matter and vacuum (which affects small strangelets more than big ones), and (b) screening of charges, which allows small strangelets to be charged, with a neutralizing cloud of electrons/positrons around them, but requires large strangelets, like any large piece of matter, to be electrically neutral in their interior.The charge screening distance tends to be of the order of a few femtometers, so only the outer few femtometers of a strangelet can carry charge.The surface tension of strange matter is unknown.