Modern military aircraft generate and move an enormous amount of electrical power throughout the airframe to supply all of their avionics and weapons. Power systems take up a lot of space.

The A-10 is an old school design, and there was no use case for installing large power systems when it was originally built. Unlike some other ancient airframes which had the spare room to retrofit power systems, the A-10 had little room to spare in its original design for a modern power system.