[exabrial]

The driver is logistics: You can package peanut butter in plastic, and if there's something like, a shipping crisis or pandemic, it can sit in a warehouse for months without spoiling.

If you can solve that problem cost-effectively, plastic packaging would disappear quickly.

[krolden]

Why would it last any longer than in a glass jar?

[exabrial]

Glass also presents a logistics problem: It's quite heavy/dense! You can save a lot of fuel costs with lighter packaging, and it makes handling pallets of goods much simpler. A pallet of peanut butter in glass would require a motorized hydraulic jack, whereas in plastic could probably (guessing) be moved with a normal pallet jack.