per grid operator PJM Interconnection:

    PJM's outages are higher than the grid planned, Mul added,
    saying there is less flexibility in the PJM system than a few years ago
    because of power plant retirements and a surge in demand from data centers.

In the above statement, PJM indicates that plant retirements are a primary driver of 'less flexibility' and these outages.

But we also have renewable sources that can't get connected to the grid - which seems like an odd problem to have in the face of plant retirements.

     connecting new energy projects to the grid, known as interconnection,
     has become a major bottleneck, slowing the deployment of new renewable
     energy sources.

ref: https://www.cfr.org/articles/us-interconnection-challenge-wh...