I was discussing the beauty of old Hindi film lyrics with a couple of friends here and the following observation came up: Most of these songs use some Urdu word or the other.
There seem to be two reasons for this. First, the “softer” sounds in Urdu are well suited to convey the sort of emotions usually expressed through songs (love, sadness etc). There is in fact a field of study called phonetic grammar where one looks at word choice from the point of view of how it sounds. More on that later. The second reason I can think of is that a number of lyricists working in the industry (past and present) are/were Muslim.
There are, however people (living in eastern UP or thereabouts) who speak what they call Shuddh Hindi, which doesn’t involve words borrowed from Urdu. But how many songs can you think of in Hindi films that use that form of Hindi? I can’t think of too many.
The first one that came to mind was Chandan sa badan. Nain ladh jai he from Ganga Jumna is another although I don’t understand the dialect well enough to be sure.
Can you think of anything else?