Look at it this way, a contribution from the outside that has a restriction (time or specific purpose) must be listed as Restricted for good reason. A NFP must show external users of their financial statements that they are properly using their resources.
Here is why you recognize a revenue and expense at the same time. As a FOR-profit enterprise, you have to match expenses to revenues to explain how you reached Net Income, yes? Generally. For a PRIVATE NFP enterprise, the point of emphasis isn't profit, but how you are using your resources.
As an aside, I think you may be getting hung-up on what makes something an expense. Think of these things more as activities that you have to describe using GAAP syntax. You capitalize “costs,” or economic activities, of PP&E to get that long-lived asset ready to produce an economic benefit to your company. Whereas, you expense something simple maintenance because you aren't building an asset. An asset is just some thing that you expect to eventually bring you cash. Often that is expected in the long-term.
Now, let's get back to donated professional services. Like I said, for a private NFP, you recognize a revenue and expense on the Statement of Activities (versus a Income Statement) because you have to show to the outside world how you are using your resources.
There are two transactions that are recognized at the same time. As an example, once you're a CPA you could donate your bookkeeping or tax services to a local soup kitchen. First, you recognize “prepaid asset” to be used for bookkeeping services. That is an increased asset. Second, you recognize the economic activity which is the expense. On the Statement of Activities these things wash-out, but outsiders see how you're using the resources.
These donations are UNrestricted donations. There is no time-restriction placed on the bookkeeping services, right? You're just donating them. The soup kitchen would need them to support their enterprises. This donation is different from giving money (other revenue) for the NFP to buy a bunch of Campbell's Soup cans.
Hopefully, this helps