Because of a "free-rider problem", small shareholders are rather passive. On the other hand, activism from large shareholders can be expected as the benefits of monitoring may exceed the costs. In particular, pension funds, which are essentially interested in maximising value, play a positive role.
CHARLETY-LEPERS, P. (2000). Activismes des actionnaires : le cas particulier des fonds de pension. In: La mutation du contrôle de gestion. 1st ed. Éditions d'Organisation, pp. 37-39.