CROSS JOIN VS INNER JOIN

Why does the kernel sometimes use CROSS JOIN and put the join condition in the WHERE clause, yet other times choose an INNER JOIN with an ON clause?

For example, the view SALESLINEEXPANDED joins 1:1 to CUSTPACKINGSLIPONTIMESTATUS and INVENTDIM.  With a significant number of records and a CROSS JOIN and a complex WHERE clause, the performance is beyond terrible.

I assumed it would only do that when the relationships were both 1:n, but in the query for SALESLINEXPANDED, they are both 1:1 as are all of the other joined and left join views and tables.

Curious.