Copying some comments by @byzantinist on discord that help explain.
If you opt for 10 Tracts there is no guarantee of a Castle. And no guarantee the 10 Tracts will be in the same Region (they will probably be in different Regions). If you opt for 1000 Plots there are no guarantees of any Keeps. And they will likely be spread among different Tracts and Regions.
The main advantage to 10 Tracts or 1000 Plots is they can be distributed immediately and so you don't have to "trust" the token holder for a year until lands are released
Also putting a small upvote on my original comment for visibility.