In a base 10 system, numbers that end in zeros, particularly a lot of zeros, feel like significant milestones. The block height will begin with an 8 for almost 2 more years, so that change of appearance is also significant.

When we reach block 1,000,000, that will feel even more significant, since it will be the first time ever that we'll have a block height made of 7 digits, and another 19 years or so after that before the block height will start with a 2.