April is George Takei's birth-month.
They look to be all Takei/Sulu and Janeway focused books for April.
I was looking at the April sale page just now. I don't recall this being on the page before (but my apologies if it was there and I've just forgotten), but now they seem to be actually calling out the reasons the various books were included in this month's sale, and
@Corran Horn was exactly right on the reason for the Sulu-focused books.
Strangers From the Sky
- Celebrate First Contact Day on April 5th!
(I am very happy to be getting this book as part of this sale, but the
First Contact novelization would have also been an obvious tie-in to this one!

)
The Eternal Tide, Echoes and
Mosaic
- Celebrate Kate Mulgrew's birthday on April 29th!
To The Stars, The Fearful Summons, Forged in Fire
- Celebrate George Takei's birthday on April 30th! (MA says April 20, so I'm not sure which is correct?)
Flashback
- Nothing specifically mentioned, but does feature *both* Sulu and Janeway, so...
I wonder if commemorating specific dates is going to be the general theme for all their 2020 sales? If so, what might we possibly see in May? According to MA, there are actually very few main character performers with birthdays in May:
- Colm Meaney (Force and Motion?)
- John Billingsley (Live by the Code?)
- Doug Jones (Fear Itself?)
(I didn't check Kelvin Timeline performers, since there are no books other than the two novelizations, and I didn't check
Picard performers, since there is only the one book so far.)