This is all about the available technology for DJs.

Remember back in the days, you had to get your tracks on vinyl, and usually fill them too (not sure about this). This meant long beat sections in order to fill out that vinyl. Also, there was no mixed in key, so the DJs relied on long beat sections in order to not have awful sounding transitions. Now, with CDJs, laptops and whatnot. More melodic content can be added to the first minute, and DJs don't need a lot of time to beatmatch. All of this again makes producers and artists more free to do as the please from a creative perspective. They don't have a format to fill, DJs usually have mixed in key, and the waveforms/rekordbox makes you able to plan rather than rely on the "2 minutes left of track" mark.