Dropping linking R's from the middle of the words [closed]

Why does it exist and whom is it typical for? Is it the feature of the past century?

I noticed Americans to do it. There are two examples coming to my mind, dated 1960s. The first one is the verse from the song ‘Moon River’: wherever you're going, I'm going your way. Frank Sinatra doesn't pronounce the first R in wherever, neither does Audrey Hepburn in Breakfast at Tiffany's — a British, but singing it in American way (it's at least about the -ing endings). The second example is Christopher Plummer (Captain von Trapp) in the film ‘The Sound of Music’ (figured it out that it's not him singing though, it's another American singer). He's singing the song Edelweiss, and the word forever is repeated many times in it. So he also says /faw evah/ every time.

In both "forever" and "wherever", I think there is some uncertainty as to whether we are dealing with one word or two. Conventional spelling is not a certain guide, so just because the words are written with no space before "ever" doesn't tell us for sure. Syllables in English end where words do, and r is lost at the end of syllables, if it's really "for ever" and "where ever", we'd expect r to be lost in a r-less dialect. If it's really "forever" and "wherever", r should remain.

I suggest this is the source of the variation among singers and dialects.