Thoughts on why these have oil canned ?

This long runs, and some shorter ones as well are all oiled canned. Installer said it was the ply underneath but given what I saw about how it was installed, I have doubts.

Some of the panels I saw were fixed in place without being flat etc, so my guess is the installation method was sloppy. Also some of the panels had visible canning even before they were installed.

Would appreciate opinions from those who do this every day.