Mordona has accurately reported the dev's stated reasoning for mandating a server connection.
However, what anyone who pays for (or even just plays) v17 should at least consider is that testing a high-score board in no way requires the dev to force anyone to connect to a server.
Any possible multi-player features the dev may want to test can easily be gated behind an optional server connection. The excuse of "I just want to give you this extra content, so just connect here, don't worry about it" doesn't really make sense.
However, there are other goals that can only be achieved by making that connection mandatory. Aside from the obvious data safety concerns, enforcing the server connection prior to game launch ensures that players (including paying Patreon supporters) don't actually have any ownership of the end product.