"It's not that good" - That's rather subjective, but you're trying to spin it like the majority of people think that it's not good, If it wasn't that good, it wouldn't have made it to number one. The fact that it did shows that a lot of people quite liked it and liked it enough to share it, download, it or stream it.
It's still number one because it's still popular with many people.. why did any song go to number one, ever? Because every song that went number one is because a lot of people loved the music coming from those particular singers/bands.
You clearly are biased against the other artists that you mentioned, and quite bothered that a collab with Billy-Ray Cyrus became more popular than the music you enjoy the most, you see it like they're infringing on your faves success.. but obviously it hasn't diminished their talent and success, Post-Malone has been very popular with a lot of people, and most of his songs have gone to number one, same with Camila, and Taylor Swift who each have made it to number one in their careers.. but it comes back to the fact that a county singer and a rapper joined up to make a unique, but different song that hasn't been done before and instead of being applauded for bringing about a new music collaboration..you're stuck on the fact that one of your faves didn't get a number one this time around. All the outrage against them is just a huge tantrum and it's pathetic.
Try and move on, because it's not a big deal. Another song will become number one and dethrone it, who knows who will, but people need to stop obsessing over number one's and chart positions, that doesn't determine who's more or less successful, it just shows which song is the most popular at the time.