Because miners on the other side of the world don’t hear about the latest block until much later than other miners? Miners who hear about it first get a head start mining the next block. If the delay is significant, you get a single mining cartel.
Mining a block is suppose to be a lottery, not a race.
Thanks for the clarification here. I've read a lot of your comments today, and this is the first time I've understood your point.
I've learned a lot, btw... so thanks for that too.