No reason? It's probably meetings, then more meetings, add some meetings, and you guessed it, meetings.
Like the follow tab mentioned it's probably first product owners meetings to agree on what a user would expect.. and there's always someone having a wild opinion or two that needs to be "hashed out". Then when that's done it's meetings with the UX team, then they have a meeting on their own, then a new meeting with product owner, UX and designers, then after that frontend team is in the loop, then back to UX and prod owner, then a new round, then it's time for backend to come in, first one with PO and frontend, then a technical one to agree on how to do it, then database team is involved, they refuse to change a small thing and expected functionality needs to be changed, back to PO, UX, frontend, backend, and then finally maybe a dev or two can sit down and add it. Which takes 2 hours. After six weeks of meetings.
And then comes testing of course, and signoff on the functionality.
"Fast" is nowhere in enterprise development.