Passage: Schmit sang the lead vocals on the song, with Frey and Henley singing counterpoint. Schmit also played the bass on the track, which has the distinctive bass riff believed by Schmit to have been devised by Frey. According to Henley, Frey came up with the counterpart on the song, and played the guitar solo on the song.

Question: Based on this passage, who sings i can't tell you why by the eagles?
Steam of consciousness below:
The relevant information is: Schmit sang the lead vocals on the song, with Frey and Henley singing counterpoint.
So, the answer is Schmit sang the lead vocals.