Even 18 years ago bbc.com redirected to bbc.co.uk. Just checked the Wayback Machine.
If I recall correctly, initially anything bbc.com just diverted to the main BBC homepage, all the content was on bbc.co.uk addresses, there were no redirects.
The same was true if you didn't use www.bbc.co.uk,
without the www it went to the homepage
Mind you not quite sure which domain they want to use isn't new, since they had the old bbcnc.org.uk addresses, later replaced by bbc.co.uk and then for some reason they acquired bbc.com. Whether it was used for anything I couldn't be sure but it seems to be a duplicate of the .co.uk.
The reason they bought the .com domain was because outside the UK, especially in America .co.uk addresses aren't well known. I think it was first really noticable on 11/9/2001 when lots of people tried to find the BBC website for news and went to the website of Boston Business Consulting.
This was around the time of the .com boom but even now people just expect a big organisation to be something.com