The most honest and direct answer to your question, the one Pittsburgh Redditors will hold their breath and stamp their feet about, is the public sector unions are in charge of the route 28 projects as they are all road projects. And that's why it's been in a constant state of repair since the day it was "completed."

Much of the transportation infrastructure in Pennsylvania was designed and built during the Great Depression and years immediately afterward when government projects were planned with one of the criteria being creating as many busy work jobs as possible to get and keep people employed. Tunnels and bridges especially were proposed and built where road ways around the obstacles would have made more sense, and very frequently simpler and more direct proposals were dismissed in favor more elaborate and complicated systems that require more maintenance precisely because they would employ more people then and into the future.

And now we're stuck with many of those decisions.

Stuck with them not always because there aren't better solutions or ways to correct the design flaws, but stuck with them because proposals to replace the bad ideas, like the Parkway East Bypass that would eliminate the bottleneck the Squirrel Hill tunnel creates and has been proposed and re-proposed again and again since the 70s', would mean far fewer jobs for Penn Dot in the future. Same with rt 28, many proposals have been made and dismissed to replace that road with others that make more sense, but Penn Dot and the politicians they support prefer to keep things the way they are precisely because it keeps the money flowing to them and serves another of their political interests ...

... that being population control, down vote away but it remains true none-the-less;

Back in the 80's Pittsburgh hosted a convention for some Society of Transportation Infrastructure Engineers (or something like that I can't recall the exact name) where they "awarded" Pittsburgh with the title of worst transportation infrastructure in the country. Not because of the condition of the roads, which if you can believe it were even worse than they are today, but because of what the engineering group called the "Berlin Wall approach" to population losses by local politicians. They cited numerous examples where transportation money was used to build/upgrade/change road ways, one of which was ... drum roll ... rt 28, in the least efficient and most disruptive way possible with the idea being that if they made it as difficult as possible to get in and out of the city that would dissuade people from moving out to the suburbs in increasing numbers as they were back then.

Obviously that didn't work but even in more recent years that "Berlin Wall" approach has been repeatedly employed to make commuting into and out of the city deliberately difficult. More recent examples being, federal money that was allocated to extending the light rail system out of the city to serve the expanding Pittsburgh International Airport project in the late 80's being instead diverted by local planners to a bus way projected instead, the decision to do so resulting in the head of the regional transportation committee at the time to resign and take a similar job elsewhere (in Atlanta I believe) with a public letter EXCORIATING local politicians and planners for choosing an already "obsolete" plan over real modernization for the purpose of serving the interests of public sector employee unions over the needs of the region ... that bus way btw was obviously never built. Other examples are the money intended to increase access to Oakland from downtown (the forever proposed Spline train and similar) and proposals to deliver light rail to the North Hills and beyond instead being used to build one of the biggest boondoggles ever (voted that by numerous watchdog groups) the LTR tunnel connecting the Northside stadiums.

Like it or not, the rt 28 project like all of the transportation projects in the area are under the control of political interests who think punishing people for choosing to live outside the city by intentionally designing inefficient and obsolete transportation systems and keeping them in a constant state of disrepair to the benefit of public sector unions is a legitimate function of the government.