Author confirmed it via blog posts last month:

• https://mypage.syosetu.com/mypageblog/view/userid/397971/blogkey/2602726/
• https://mypage.syosetu.com/mypageblog/view/userid/397971/blogkey/2608227/

From what I can gather from Deepl and Google translate:

• Reasoning from the publisher was that it took too long between volumes.
• Author contacted the publisher at the end of May 2020 but they never responded.
• Author contacted the publisher again on July 6 and was told it was discontinued.
• Author has quit writing over this. Describes themselves as a 'Retired Writer'.
• They go pretty deep into what 'work' means to them, how much they enjoyed it and how they didn't want to compromise on the vision they had. They see 3 pillars to successful work: Satisfaction, relationships and reward.
• At one point they had some issues (physical and mental) to work on that slowed the process. They mention they were unhappy at this time.
• They were excited when a manga adaption was brought up but they had some issues with the first adaption.
• By the time the second manga adaption (sequel) came around they had lost 2 of the 3 pillars. They felt the satisfaction and relationships had been destroyed. They stuck it out despite that for the readers.
• The publisher owns the work until December 2022, they won't renew the current contract.
• The publisher will not be reprinting any volume. The author describes the publisher as 'evil' as they didn't reprint previous volumes that went out of stock.
• Digital versions will still be sold for now.
• Still working out terms with the publisher regarding the future of the manga adaption.
• "That said, I won't stop readers from complaining because I think theirs a legitimate reason to do so. Please say what you want and make them regret it."

The publisher is Futabasha under the M Novels F imprint. J-Novel Club is currently releasing the series in English.