Size increase of .sppkg packages with heft/v1.22

After upgrading our solution to SPFx 1.22.rc-0 and switching to the new heft build toolchain our .sppkg packages have suddenly grown massively in size. They are more than double the size of the 1.21 version. Is there a reason for this? Is there anything we can do to reduce the package size back to what it was previously?

Our main solution contains both web parts and list extensions, split into several bundles. Let me know what other details would be helpful.