Why did readers find Robert Browning’s Sordello difficult to understand?

Readers found Robert Browning’s 1840 poem Sordello difficult to understand primarily because it was densely written, featuring multilayered meanings and numerous historical and literary allusions.1

The work made exacting demands on a reader’s background knowledge, requiring a considerable acquaintance with its subject matter to be fully grasped. Furthermore, the poem’s style contributed to its reputation for obscurity; Browning’s use of elliptical syntax and his attempts to replicate the irregular, broken rhythms of speech made the verse challenging to read quickly. Upon its publication, these factors led to the poem being almost universally declared incomprehensible and a critical failure.231