Missing kernel source files in linux-hwe-5.x-source-5.x.0 packages

I did not find the linux-source-5.4.0 package for HWE 5.4 kernel in Ubuntu 18.04 (bionic).

Similar packages for previous kernel versions exist: linux-source-4.15.0 for kernel 4.15 and linux-source-5.3.0 for HWE kernel 5.3.

I found a package named "linux-hwe-5.4-source-5.4.0", with similar description like previous versions, saying:
 This package provides the source code for the Linux kernel version
 5.4.0.
But it does not contains the "/usr/src/linux-source-5.4.0/" tree.

$ dpkg -L linux-hwe-5.4-source-5.4.0
/.
/usr
/usr/share
/usr/share/doc
/usr/share/doc/linux-hwe-5.4-source-5.4.0
/usr/share/doc/linux-hwe-5.4-source-5.4.0/changelog.Debian.gz
/usr/share/doc/linux-hwe-5.4-source-5.4.0/copyright

In contrast, the package linux-source-5.4.0 in Ubuntu 20.04 (focal) still has the "/usr/src/linux-source-5.4.0/" tree.

In addition, the linux-hwe-5.x packages (e.g., linux-hwe-5.13-source-5.13.0) in focal have the same problem.