Bobby - I'll preface this by saying this has ABSOLUTELY nothing to do with who is playing the role of Brenda, but your comment of "I think they're really missing out on the why and how of what he did. "
Have you read the book? Not the book to the musical. The biography of Frank Abagnale Jr?
Because if you had - this isn't a question. The main driving force behind what he did (despite what was in the movie) was to get women. He was a womanizer and loved the attention of women. That's the majority of the reason he did what he did and for as long as he did it.
So I don't think (I know I haven't seen it yet) that having all the womanizing stuff in defeats the purpose in indicating why he did what he did. And furthermore - having a love interest is a complication in his desire to not have any attachments and go where he wants to go and do what he wants to do.
It's still a musical afterall - which most of the time requires a love interest.
"A little nonsense now and then is relished by the wisest men" - Willy Wonka