There are plenty of people in transit agencies, city DOTs, and MPOs who know basic urban planning principles very well. On the rare occasions that these people are empowered, great things can happen.
The problem is that elected officials call all the shots and they're more likely to listen to, well, pretty much everyone except nerdy planner types. Instead, special interest folks like Roger Romanelli get in the ear of electeds, and it's their priorities that drive the investment decisions.
I bring up Romanelli because he just started this wacko astroturf "Westside Coalition" to try and get $2B in Federal infra money to rebuild the Lake St L, all for the benefit of a few industrial businesses that want easier semi-truck deliveries. To disguise their intentions, they came up with a list of low-value or mid-value transit projects that clearly won't get built. Extending the Blue Line to Mannheim isn't on their list, but it's kinda sus that it shows up in a news article right now after fading away for years. Note: Romanelli lives in Hillside near the proposed Mannheim CTA terminus.
http://www.fixthewestside.com/