Why is dl.flathub.org/repo/appstream/io.github.chidiwilliams.Buzz ⪆ 3 / 6 GiB?

[RokeJulianLockhart]

       Ref: app/io.github.chidiwilliams.Buzz/x86_64/stable
      Arch: x86_64
    Branch: stable
   Version: 1.2.0
   License: MIT
Collection: org.flathub.Stable
  Download: 3.0 GB
 Installed: 5.7 GB
   Runtime: org.freedesktop.Platform/x86_64/24.08
       Sdk: org.freedesktop.Sdk/x86_64/24.08

    Commit: 6070a19f9261c2317ae7acaedd02f0251aa87d8dd3dc6b2cbd72337389d0828f
   Subject: Moving buzz-captions to main manifest (7380beb4)
      Date: 2025-02-25 16:33:10 +0000

3 GiB compressed, to ≈ 6 GiB uncompressed is significant. Not even Flatpak inherently causes this. What does?