Despite contacting support I haven’t managed to obtain a reply as to why yet. To be clear, they haven’t just de-listed it, they deleted the product, which means that the reviews for it are gone too.
I’m going to wait for them to tell me what the problem is before trying to re-list it.
Considering that Linden Lab moderates the Marketplace solely through user reports, whoever you are, I hope you are proud of yourself.
In the meantime, it is still available from the in-world store if you want one.