The bitcoin blocksize limit.

Bitcoin’s current blocksize limit is 4MB, which means the blockchain grows at about 200 GB per year.

Whenever someone syncs a brand new bitcoin node, they must download and verify every single block in bitcoin’s history, dating back to the Genesis Block.

The faster the blockchain grows, the harder it is to sync a full node, meaning fewer and fewer people do it, and eventually the blockchain is only run a handful of small entities (Google, NSA, etc.) in centralized data centers.

The big blockers (Roger Ver, Craig Wright, etc.) wanted to raise, and perhaps even eliminate the blocksize limit altogether. Over the long run, this would be a disaster of epic proportions and lead to the failure of bitcoin altogether.