Why are new encyclopedias being published when there is Wikipedia?

There are a number of specific policies and practices of Wikipedia that reflect judgment calls, and it's perfectly reasonable to treat them differently for different projects:

• Above all, creators of another encyclopedia might want to exert editorial control over the product. The rest of this list expresses some of the specific ways they might do that.
• Wikipedia explicitly aims to serve a general audience; another encyclopedia might be designed for an expert (or afficionado) audience in a certain field
• Wikipedia contributors may be anonymous, and the majority are
• Wikipedia maintains a strict egalitarian ideal, which makes it difficult for subject matter experts to exert special authority
• Wikipedia's peer review mechanisms are very specific; publishers of another encyclopedia might design them differently
• Wikipedia's standards for sourcing, and its threshold for inclusion, are very specific; publishers of another encyclopedia might design them differently
• Wikipedia has very specific standards around copyright of text and media

On my connections to Wikipedia: I have been editing Wikipedia (almost exclusively the English language edition) as a volunteer since 2006. I designed the first formalized program to support university instructors assigning Wikipedia composition, on behalf of the Wikimedia Foundation, in 2010. I have run a Wikipedia training and consulting company, Wiki Strategies, since 2009. I have served as editor in chief of the Signpost, Wikipedia's volunteer-run newspaper, since August 2016.

Because of its anonymity, nobody is ultimately responsible for the veracity of the information. This is one major point which makes Wikipedia vulnerable and of limited sustainable reference value. That is not to say that there are not excellent entries there. Unlike free software, there is no easy way to say that the article is wrong on less well-understood or contentious topics. An authored article at least has someone with a reputation to lose on the producing end of the text. Plus, if you know the reputation of the author, you can judge how far you want to follow him/her.

You don't want to rely on one way of doing things for something that crucial. Every way of doing things, however great, has its weaknesses. For a robust provision of such crucial services we need different systems to coexist and compete. That is the big contribution of Wikipedia; it improved the robustness of the system by adding another way of doing things. However, it should not undo that benefit by becoming too dominant. Not that I see any immediate danger of that happening, in part because of the reasons mentioned by @CaptainEmacs.