Music theory question?

So, I was watching a video on the computer generated beats that newer songs tend to use. The guy in the video was discussing how using drum tracks takes away actual musical talent. BESIDES THAT....He also went on in the video to say this...”I understand that all music that has 4 beats in a measure, is going to emphasis beats 2 and 4”. My question is what does he mean by that? Why would they emphasize beats 2,4 and not let’s say 1,3? Here is the image from the video, I cannot make sense of it? Thanks for the help!