I have a harder time understanding why any "solo miner" would pay 2% to some "service provider" rather than mine on its own.
I suspect that this is probably the biggest reason:
Solo.ckpool.org is extensively connected to high speed low latency bitcoin nodes for rapid block change notification and propagation.
Solving a block is only half the battle. First, the software that is building the block headers needs to hear about solved blocks as quickly as possible so you don't waste time mining a stale block at a height that is already propagated to a significant portion of the network. Then, once you do solve a block, you need to get it propagated to the majority of the network's hashpower before anyone else does the same.
[...]
I may be missing something, but how does connecting to ckpool "lower" any latency? The block header is 80 bytes, and AFAIK most miners are okay with mining an empty block on top of a valid header for a few seconds because "Who the heck would produce a valid header without a valid merkle-root?" Sure, the previous block needs to be downloaded completely to figure which transactions to include in the next block, but we are talking about 2% fee.
So high speed (which I assume means "high throughput" in this context) seems practically (if not completely) unnecessary. Then latency being the main (arguably only) important factor, I remain unconvinced.