Checkdb (and other maintenance types of tasks) almost always cause drops in PLE just due to those procedures reading a lot of pages into the buffer pool and then they get dumped back out to accommodate for the next batch. So a page doesn't stay in the buffer pool that long while those are going on for most databases.

You very well could have a system where tempdb just doesn't get hit too hard or too often. I've had some of those but I still create at least 4 files for tempdb. If nothing else, it kind of forces us to have to get a better handle on the storage available, in use, etc and get a bigger picture view of that side.
And someone will eventually do something like a union with the largest tables on the server. And want it ordered. Or import a bunch of large files into a temp table with several LOB columns. And then add an index on the largest columns of the table.
But enjoy it while it's quiet. For now. 🙂

Sue