A traditional newspaper was an organic part of a community. Most of its reporters, editors, and management were local to the newspaper's publication area, and so most of its political 'slant' was a reflection of the values of the community it served. In metropolitan areas there would be competing papers with different slants — each paper being drawn from and serving a different segment of the community — but for reasons of competition they would all try to keep in line with the community as a whole, which prevented them from becoming overly radicalized.
This 'slant' was maintained by a feedback process with the community as a whole. Editors were aware of sales figures, they got feedback from the public in both published and unpublished communications, they knew which articles were popular and which unpopular; Editors generally had a clear 'sense' of the mood and attitude of the community they served, and avoided publishing editorial material that ran significantly against their community's value structure. News was a separate matter in traditional newspapers; most newspapers kept fact and opinion segregated into different departments.
As media technology has advanced, providers became capable of simultaneously extending their reach and targeting their audience, so that now we see media sources that are tailored to widely dispersed and politically homogenous groups, groups with increasingly radical (one might say bizarre) viewpoints. Such groups are no longer rooted in any particular organic community, but representative an abstract political community which has no allegiance or connection to anything outside itself. The same feedback process applies, but such cases become true echo chambers in which the provider and the abstract community feed into each other: a small-group dynamic called 'The Risky Shift' where people compete to present the most dramatic or aggressive perspective, not the most reasoned.