Well, he still goes to help Joanne, so they haven't taken that part away. I thought that it was because of something to do with film versus theatre. On stage, you can have one scene that encompasses three different locations, and it won't look weird. The loft can be center stage, Collins on the street can be stage left, and Joanne in the lot can be stage right, and you don't really think that's weird. On film, it might be too cumbersome to cut back and forth to her, or something. I suppose Mark could've just answered the phone and the "Maureen, I'm not a theatre person," could've gone, but it will still make perfect sense without those lines.
A work of art is an invitation to love.