It was the first choice for many companies. In the Delphi development world (starting in 1996), NNTP was pervasive and almost every company related to the 3rd party ecosystem ran an NNTP server (we still do, it provides both NNTP and web access to the same message store).
Believe it or not, the issue wasn't as much the servers not being maintained any more, it was the clients. Various clients, especially email clients, stopped providing NNTP support alongside POP3/SMTP/IMAP.
Just a reminder that the d programming language forums are architected on the back of nntp:
I've never understood why private news servers and groups never caught on. Company newsgroups on a company news server seem to me to often make a lot more sense than company mailing lists on a company mail server or company forums on phpBBB or similar.
News readers generally do a much better job than mail client of organizing discussions into threads, and the hierarchical structure of the newsgroup namespace fits well with the way most companies and projects are organized.
Nowadays the argument for NNTP is weak because the decline of Usenet has, I believe, reduced the number of good, maintained NNTP clients. But I don't understand why NNTP wasn't the first choice for these things 15-20 years ago.