From asl3-asterisk / docs / build-asl3.1.md :
Action : install
The install action performs a "make install DESTDIR=/" in the merged directory.
Note: this action does NOT include everything in the "asl3-asterisk-*" packages. The focus is on executables (e.g. asterisk) and modules (e.g. app_rpt.so, chan_simpleusb.so, etc). The assumption we have made is that you are working on software (code) changes and you wish to test them on a system that already has ASL3 installed.
In your case, you do NOT already have a system with ASL3 installed. We use the debhelper (dh) command to create packages that includes all of the needed bits with the debian/rules file controlling what gets included in the .deb files. We don't have a standalone command for installing to a clean system.
Since you are bootstrapping, you need to start off with :
cd <asl3-asterisk-directory>
./build-asl3 source build package
to create a set of package files. The built .deb packages will include the missing content.