I can't answer for Jamie, but I do recall this discussion being held previously, so I'll offer my 2 cents for what it's worth.
I think we all agree that having sourced profiles is better than unsourced. No argument there at all. However, when it comes to finding a way to encourage sourcing, ultimately, there is no perfect solution. I'll lay out what I see as the challenges and perhaps can find a better way, but none of them will prevent unsourced profiles.
1) Someone comes in with the best intentions and plans to source it later - so they fill in the profile, they don't put anything in the source box, they know it will ask if they plan to source it later, they agree, it marks it unsourced, and it's flagged for someone to follow up later. IF they choose to check their unsourced profile, it will come up in a report and it will also show up in the Suggestions on WikiTree+, but both only can be seen if they go out and look for them. So if their intentions are good, and they are diligent about their follow-up, there's some hope that it will be sourced at a later time. OR, since Source-A-Thons go out looking for these profiles, we often will see these get sourced through that process.
2) The person comes in with the best intentions to source later, BUT does not like that "unsourced" tag on their profiles, as it makes them feel badly about having a huge label at the top of a profile with their name on it. So they defeat the box by typing in nonsense. Something like, "Sources to be provided at a later date". The unsourced tag never gets applied, it never shows up on any reports, and it is up to the profile manager and anyone else who stumbles across it to identify it as a profile in need of sources. Upon rare occasion, it is encountered by someone who does not have time to source it, but recognizes it as being unsourced and applies the unsourced template. These become the hidden unsourced - and it takes a relatively large effort to hunt down and locate them, but once their located, often applying at least a single source to them is relatively easy.
3) Someone doesn't care to source their profiles, and just wants to be left alone to build their tree their own way, and so they type in nonsense like, "I will add sources at a later date" or "family history" into the source box, and the unsourced tag is never applied. As above, the profile goes hidden for awhile or even a long while before it is hunted down. The profile manager never intended to source it - OR - the profile manager really doesn't understand the sourcing concept and simply avoids it because they can't do it or it's too challenging to do it. Sometimes this can be fixed through mentoring or gentle assistance, but sometimes it's a "I won't do it" principle and once these individuals are identified, decisions have to be made as to whether their contributions are helping or hurting the tree. We have numerous processes in place to address this, so I won't go into that one. - and a variant on this one is where they accept the Unsourced tag and don't care, but at least when that happens, it allows the profiles to be identified as in need of sources and hopefully during a future Source-A-Thon someone can go back and fix them.
So it's quite easy to type nonsense. I've seen (and don't get me wrong - some of these could be perfectly valid, but there's no way to verify) things like: My sources, Family History, Family Bible, To Be Sourced Later, Sources, Passed Down From My Grandma, Personal Knowledge, etc. etc. I do get that some of those could be true, but most of them could be sourced with something that can be verified instead of hearsay or nonsense. Can we mentor or even discipline those who appear to do it with bad intentions (or even those with good intentions that forget)? Sure! Once we identify them. But it's stumbling across someone with this pattern of behavior that's the challenge.
I don't know what the right answer is to help make it so that profiles can be sourced with more consistency, but I will agree that whatever process is put into place will have loopholes and someone will exploit them - both with good and bad intentions behind them.