The intro can vary depending on the level of the artist. If they are established, longer intros can be used. But rarely much more than 15 seconds are the rule. Radio has 22 minutes of commercials an hour, so finding ways to cut every second out of a song is pretty normal. And the "ten second intro" is very true for almost all NEW artists. The basic listener has an 8 second attention span. Watch anyone around an "Echo Dot" saying "Alexia...play" they are on to other songs so fast it makes your head swim.
Again, most music now is background, so the longer intro is just one more reason to tune the song out and move on to a next one.

MAB