Because:
The DistroWatch Page Hit Ranking statistics are a light-hearted way of measuring the popularity of Linux distributions and other free operating systems among the visitors of this website. They correlate neither to usage nor to quality and should not be used to measure the market share of distributions. They simply show the number of times a distribution page on DistroWatch was accessed each day, nothing more.
So people see it on the list and click on it wondering "what the heck is this MX Linux thing". And that boosts the ranking. And now that it's at the top, it attracts more curious clicks, thus it continues to remain on top.