In the Golden Age - and the years before and after - most orchestras were named after the leader of the orchestra.
The orchestra leader was either conducting the orchestra, like D’Arienzo and Canaro did, or he was playing in the orchestra,
like Di Sarli, Pugliese and Biagi did. In both cases, the orchestra leader was the artistic leader of the orchestra, and he would be regarded as the front figure
- more so than the singers, who changed orchestras frequently and often were regarded as just another musician.
Like mentioned above, most of the orchestra leaders composed music. But there were lots of other composers that contributed to the orchestras' repertoire. We don’t refer so often to these composers or connect their names to songs. In this respect, we think differently of tango music than we do with the music of classical composers. Most of the popular tango compositions were actually recorded by more than one tango orchestra, like in classical music, but in tango, we still mostly refer to the orchestra, not the composer. In this sense, the tango orchestra was more like a modern pop band.
Example classical music: "Ode to Joy" by Beethoven. This piece, part of Beethoven's 9th symphony, is recorded by many symphony orchestras, but when we hear it, we mainly think about the composer. Often, we don't even know which orchestra who is playing, or who the conductor is. Symphony orchestras have different conductors, and the orchestra isn't the conductor's "property", as it were.
Example tango music: "Qué noche" by D'Arienzo. He didn't compose the piece, he just recorded it with his orchestra, but we still connect it to D'Arienzo and don't usually mention the composer.
Fun fact: D'Arienzo recorded "Qué noche" two times, thirty years apart. Listen on YouTube:
TANGO NOTES has got a D'Arienzo page with discography and listening examples here.