What's the point of doing (ETS/ATS) World of Trucks External Contracts?

There are three points I'm aware of:

• Fulfilled external contracts show up in your public profile on WoT, which is basically just statistics.

• You earn achievements for the external contracts.

• Every now and then SCS runs Community Events that require you to fulfill external contracts (in this case, the Operation Big Sur requires that you complete at least 15 deliveries from or to the construction site on Route 1 in American Truck simulator). Please note that Community events are optional.

"World of Trucks is envisioned as an optional layer created alongside the existing single player game." - SCS Software

Source: http://blog.scssoft.com/2015/12/world-of-trucks-contracts-questions.html (very early Q & A).

Additionally to the things pointed out by Gerald, a few other things are,

• "Special events" on World of Trucks only work with WoT contracts (e.g. During Christmas 2016, you could deliver giant gift boxes on trailers for unique paintjobs and other accessories).
• There are no important or urgent (Just in time category) deliveries.
• There's no deadline or estimated delivery time, you can't be late (for the same reason as above: this feature was dropped due to feedback received, as the always running World of Trucks service advancing time, while your shut off game would not).
• WoT contracts will be suspended if the service goes offline (e.g. for maintenance), and can be continued at a later time without penalty.
• Accepting a contract will drop the trailer for pickup immediately, you don't have to stop at the entrance of a company's place anymore (very convenient).
• Not all kinds of cargo are available as in the regular freight market.
• Although trailer types and skin might change with mods, only vanilla cargo types will be available through WoT.
• Cities added by map mods will also not have WoT contract available, only vanilla cities.
• The "trailer browser" also seems to be unavailable.