1 block is added to the chain approximately every 10 minutes. That means at most 6MB per hour, 144 MB per day or ~52.5 GB per year. Where do you see an exponential growth here? Even if we consider Segwit, or even if the block size is further increased in the future, that's still a linear growth. I'm not sure how you came up with petabytes, with current growth we'll reach 1 terabyte in about 20 years, that means 20K years you reach 1 petabyte.

Now, even if your calculations were somehow correct, I'm not sure why that would result in centralization. Bandwidth is a much tighter limit than storage. Reaching those numbers in the near future would require a huge bandwidth. If such bandwidth would be maintainable by enough people then surely storage would be cheap enough and most people would still be able to run full nodes.