The Gagaku music often heard at shrines and on TV every New Year's Day is called "Etenraku".
Gagaku is a music that even Japanese people do not often have the opportunity to listen to, but in fact there is a vast repertoire of this music.
The origin of "Etenraku" is still uncertain.
It is said that it was originally performed at entertainment events held after ceremonies at temples.
In other words, it is not a music especially associated with the New Year.
However, "Etenraku" is certainly the most famous of the many pieces of Gagaku.
“Etenraku" has a particularly short melody and is easy to listen to.
As a result, it has been arranged into songs such as "Kurodabushi," popular songs, and hymns.
“Etenraku" has this short and catchy phrase.
Therefore, it is difficult to arrange ordinary Gagaku, but only "Etenraku" must have spread to the general public.
Japanese people do not usually listen to Gagaku, but they want to listen to traditional Japanese music at least during the New Year's holiday.
They think that Gagaku is the most traditional Japanese music.
And they only know "Etenraku" when it comes to Gagaku.
This is why "Etenraku" is used for the New Year's holiday.
Incidentally, to be more precise, there are three types of Etenraku:
“Hyojo Etenraku” “Ohshikicho Etenraku” and “Banshikicho Etenraku”.
Each of them sounds completely different.
The most famous of them is “Hyojo Etenraku”.