Realistically, he probably found out too late how story branches increase exponentially with every option you add. This isn't prohibitive if the game only shows one LI on screen at a given time, but these girls interact with each other.
Suppose you have 4 LIs: A, B, C, and D. Individually, they can be flagged as included ("i") or excluded ("e") from the harem. That gives us the following branches:
- Ai, Bi, Ci, Di
- Ai, Bi, Ci, De
- Ai, Bi, Ce, Di
- Ai, Bi, Ce, De
- Ai, Be, Ci, Di
- Ai, Be, Ci, De
- Ai, Be, Ce, Di
- Ai, Be, Ce, De
- Ae, Bi, Ci, Di
- Ae, Bi, Ci, De
- Ae, Bi, Ce, Di
- Ae, Bi, Ce, De
- Ae, Be, Ci, Di
- Ae, Be, Ci, De
- Ae, Be, Ce, Di
- Ae, Be, Ce, De
That's 16 possible outcomes, just from whether a girl is on your dick or not.
Now, let's add the flags for pregnant ("p") or not ("n"):
- Aip, Bip, Cip, Dip
- Aip, Bip, Cip, Din
- Aip, Bip, Cin, Dip
- Aip, Bip, Cin, Din
- Aip, Bin, Cip, Dip
- Aip, Bin, Cip, Din
- Aip, Bin, Cin, Dip
- Aip, Bin, Cin, Din
- Ain, Bip, Cip, Dip
- Ain, Bip, Cip, Din
- Ain, Bip, Cin, Dip
- Ain, Bip, Cin, Din
- Ain, Bin, Cip, Dip
- Ain, Bin, Cip, Din
- Ain, Bin, Cin, Dip
- Ain, Bin, Cin, Din
Those routes are just from the first row of the previous list. Each row of the first list has to be accounted for. If he plans on rendering pregnant women, that's a lot of variations of pregnant/not pregnant characters on screen. I'd bet a penny (maybe two!) that that's a large reason he just started forcing pregnancy on everyone. That way, he only needs to worry about whether individual girls are present, which is already a pretty large task with the number of characters in this story. This example only has 4 LIs. The actual game has several pages of LIs.