B-tagging relies on the b quark being the heaviest quark involved in a hadronic decay (tops are heavier but to have a top in a decay is necessary to produce some "heavier" particle to have a subsequent decay into a top). This implies that the b quark has a short lifetime and is possible to look for its decay vertex in the inner tracker. Additionally, its decay products are transversal to the beam, resulting in a high jet multiplicity. Charm tagging using similar techniques is also possible, but extremely difficult due to the lower mass.