Some newlyweds want the boat to themselves. The whole boat for two is a legitimate choice, with one condition: the boat price is per boat, for 1 to 16 guests, and it does not fall when only two come. On 4D3N it is IDR 243,000,000 (≈ USD 14,908), which for two guests is IDR 121,500,000 (≈ USD 7,454) each. On 3D2N it is IDR 162,000,000 (≈ USD 9,939), or IDR 81,000,000 (≈ USD 4,969) each.
What the premium buys is privacy and the freedom to choose the pace: no shared sunset, no other party on the sun deck, a jacuzzi at the bow with nobody waiting. It does not buy a different cabin, since the Master Suite Ocean is the same cabin either way.
What it does not include: a guide and documentation, quoted separately on a private charter. The honest comparison is a seat at IDR 9,500,000 (≈ USD 583) per person, with a guide and photos in it, against a boat that is entirely yours.
Caveat: the 4D3N route is an example agreed with the captain.