I spent last week trying to figure out estimates about how much time we'll spend in this quarter's project - like, 3 days on the schema, 4 days on the API, 5 days on the GUI etc. Why does management think that each part of the project is separate? Oh I forgot, they're management. I wonder how much work I could've done if management wasn't so obsessed in knowing metadata about the project instead of doing the project itself 🤔

Because you break down a large task into several smaller ones that you have a better chance of estimating. You need estimations to have an idea how much it will cost and for how long each of the devs will likely be busy.

This is just the life of $$$ vs time.
I can tell you which one normally wins 😅

Management want an general idea of how long everything will take to be done, assign $$$$ to it and if the place is big enough and the price tag is high enough, convince the board of directors to fund it.

Then set a hard end date usually in line with that estimate you gave earlier in this process, SO OVER ESTIMATE, and then the project will begin off with a good steady flow, you'll get to the half way mark and management will start wanting to shrink features as e timeline is starting to become a concern, you'll then get closer to that end date and anything left that hasn't been started will be prioritised as "wtf do we actually need, vs, what can we live without" and you'll have a bunch of work left over.

Now, had you added a few days here and there in each task.... that would have given a nice buffer to play with at the end to get some of those niceties added.