Additionally, a Forest Park branch renewal needs to be timed around IDOT's Eisenhower widening plans. Although the US DOT has approved the project, no funding has been committed to that project. That being said, the Illinois Medical District and UIC/Halsted stations have been (or are being) rebuilt.
Regarding the attention paid to the O'Hare branch, this article from transitchicago.com provides a synopsis of the reasons why the O'Hare branch is getting attention. A quick review of the most recent ridership report (see pages 14 and 15) indicates that the O'Hare branch serves more riders on a Sunday than the Forest Park Branch serves on an average weekday. As of October, 2018 the O'Hare Branch served 22,424,964 riders while the Forest Park branch served 7,303,145 riders.
The Belmont station, in particular, had 1,298,661 entries as of October 31, 2018 and O'Hare had 3,340,008. The closest Forest Park branch station is UIC/Halsted, which logged 1,429,944 entries.