The project initiation and planning phase

In those organizations that do an excellent job of IS planning, why might projects identified from a bottom-up process still find their way into the project initiation and planning phase of the life cycle?

Please provide two examples.

Valacich, J. S., & George, J. F. (2019). Modern systems analysis and design (9th ed.). Pearson. Print ISBN: 978-0135172759 eText ISBN: 978-0135172841