The motivation behind such proposals have been the empirical findings that "weak" discourse relations such as ELABORATION are the most common type of relations, and that a large percentage of adjacent sentences in fact do not have any entities in common.
a corpus based evaluation of Centering theory found that only 42% of pairs of adjacent sentences have at least one entity in common and hypothesized that discourse relations are responsible for creating local coherence in the remaining cases (Poesio et al., 2004).