Often, customers who purchase these shipping options would ignore the requested 1-3 days processing time that is displayed on the site. They would instead assume that this shipping option prioritized their processing time over all other orders in the queue. After a number of complaints from those who didn't recognize this shipping option referred to transit time once shipped, we decided to remove the option.
We explain further in the topic: I ordered "Priority" or "Express" shipping. Doesn't that mean you'll process my order faster?