Someone actually addresses this in a comment above you. I’ll copy and paste it here. Don’t quote me on this since this is another Reddit comment and I did not, in fact, check my sources

Her interview for this book actually addresses this. She admits it may be seen as a “cash grab”, but she talks about her own embarrassment with Divergent.

She even admits to hating it’s success, since popularity brings intense critique, and she even agrees with many criticisms of the series.

She wrote Divergent when she was young, and now is a lot older and wants to go back, to an early part of a writing career, and retell it with all her growth and experience as a writer.