No, it is not common for community banks to require a statement of purpose for outgoing wire transfers unless it is driven by their geography; e.g. greater Miami.
The reasons to do it:
* it's easy and, I am told that if customers get a heads up about the new requirement and are told its non negotiable, there isn't that much pushback and it eventually goes away,
* it helps identify people who might be suspicious, i.e. those who would object to the requirement,
* it's helpful to receiving banks in identifying wires which might be fraudulent; e.g. it's unlikely this New York apartment dweller sold a tractor,
* it's fundamental due diligence information that explains what may be your customer's largest transactions,
* if you always ask for it then you have good cover for asking for it when you really don't understand what the customer is doing,
* some countries require it,
* some correspondent banks require it.
To me "required" means "required;" no statement of purpose, no wire. This isn't like paying a check, your bank is under no obligation to send a wire.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.