It's both. The system was not designed for the volume nor types of waste. Plastic waste causes clog more than anything, and there's an insane amount of it.

Everyone knows Philly is dumb with trash, though. The ignorance is astounding. Every walk of life, pitching their junk where they please.

Realistically, though, it is cheaper to pay folks to clear them regularly rather than to overhaul the entire system.