Why is getting info for case studies harder than writing them?

I used to write case studies for B2B tech and the writing part was honestly fine. The real pain was tracking down the devs and PMs who built the thing.

By the time marketing wants the story, half the team forgot the numbers or moved to another project. You end up Spending weeks chasing people on slack just to get basic details.

Is this normal everywhere or were my old companies just bad at documentation?