ITV axed News at Ten in 1999 because the commercial break in the bulletin wasn't bringing in much revenue. Obviously, this was because the bulletins' viewing figures were falling.
Why did News at Ten not get as many viewers in the 1990s as it did in the 1970s and 1980s?
Were there less people interested in news in the 1990s?
Its wasn't because of that, it was because of of select number of ITV companies ( Cought Carlton, STV and YTV I think) who believe if there moved the news it could have uninterrupted films and top line programmes. Alas.. there ITV broadcast less films nowadays and the show its created for the 10pm slot were pants.
Overall the number of viewers have been on a downward tend, mind you I think those news changes caused nothing but trouble for ITV including the early evening slots.
IIRC there were also a raft of 90 minute commissions that followed the dropping of News at Ten that were dropped into the 9pm slot, but that left ITV with the problem of what to do at 10:30. They'd moved the news to 11pm and put some unmemorable offerings in at 10:30.
Of course by this time the BBC had moved its 9pm news to 10pm, so ITV had to move their programme out of the 11pm slot and hence the News at When era began.
Not one of ITV's greatest decisions if truth be told.
Worth noting ITV had already committed to returning to 10pm before the BBC announced their own move to 10pm, with just two weeks notice compared to the years of negotiation ITV had to go through.
The 30-minute problem of course became apparent when they aired at 10.30pm too, with nothing of note to air at 10pm most nights. It took them long enough but restoring News at Ten back in 2008 is probably one of the best decisions by ITV since it's merger.
In terms of the general decline in news viewing figures, the lead-up to when NAT was axed in 1999 saw the beginnings of multi-channel satellite and cable TV which brought with them new competition in the form of Sky News and BBC News 24 (although the latter was not as well known at this point). Also, towards the end of the decade, the internet was beginning to be more widely available in people's homes, so the online consumption of news began at this time.
Prior to these changes, TV news bulletins like ITN and BBC News had been the main way of getting up-to-date news (well, except radio bulletins) plus the new multi-channel era meant the number of people watching TV were spread more thinly across a greater number of channels. Whereas in 1989 you only had 4 channels to watch, so the likelihood of people watching NAT was higher than in 1999.
I did find it quite amusing at the time how various broadcasters tried to jump on the NAT bandwagon as soon as ITV vacated the slot. Obviously, the BBC bulletin moved to 10pm, but Sky renamed their 10pm bulletin "Sky News at Ten" and the ITN News Channel had "News at Ten" (as well as "News at Eight" and "News at Nine"). Interestingly, when the BBC Nine O'Clock News moved to 10pm in October 2000, ITN got their own back by changing those to "The Eight/Nine O'Clock News" to cash in on the BBC's authority! It was quite an interesting time to be a news viewer in 1999/2000!