Why Not Just Make Programs Self-Contained?

[skylerclooney]

Hey everyone,
I’m Skyler, new here. A few days ago I had my first proper encounter with DLL problems, and it honestly threw me off. I was trying to run a small utility I downloaded, but instead of starting, it complained about a missing `api-ms-win-crt-runtime-l1-1-0.dll`. I had no idea what that even meant.
After some digging, I figured out that DLL files aren’t just 'extra files,' they’re more like shared libraries Windows programs call on when they need certain functions. I ended up repairing my system files and reinstalling some runtimes, which solved it, but the whole thing left me with a question I can’t quite answer:
Why does Windows prefer using these shared DLLs instead of just including everything the program needs in one self-contained package? To me it feels like having a program depend on external files makes it more fragile. Is there an actual benefit I’m not seeing, beyond saving disk space?