Thus every DVD and DVD player sold in N. America has to license AC-3 from Dolby.
The best way to steal from people is to do it without their knowledge.
The really interesting thing about AC-3 is how it is stored on a film reel. Back when it was developed, multi-channel audio was becoming a thing. For large format film (70mm), the solution was simple: 6 magnetic soundtracks. This actually far exceeds the quality of most cinema audio systems even today. But film companies wanted to get it on to 35mm film which the vast majority of cinemas could actually use. 35mm already has two optical soundtracks, and they didn't want to remove these and force cinemas to change their equipment.
One solution was to have the soundtrack stored on some other medium and synch it together with the film. This the approach used by DTS. But Dolby developed a technique to print the soundtrack between the perforations on the side of the film, thus producing a film that is completely backwards compatible and even has an analogue backup which can be automatically switched in case the AC-3 got damaged. As is often the case with technology, it wasn't the highest quality format that won, it was the one that could be practically used at the time.
AAC, while not controlled by a single company, still has its problems. AAC has had tons of stuff hacked on to it over time (I count 14 profiles), but only one license is offered. So you end up paying for things you don't use, and it's also quite expensive (4x the cost of H.264 video).
MPEG itself has a FAQ entry on "When should I use AAC rather than MPEG-2 BC?" [1]; of course the point is moot in context of DVDs. This Apple documentation article [2] lists the supported codecs and lists the relevant one as "MPEG-1 Layer 2 Audio"... close enough. It talks about how AC-3 enjoys broad support worldwide, but MPEG-1 Layer 2 is only mandatory in PAL regions. It includes language to suggest that AC-3 may not play on very old players in PAL regions, implying that at some point AC-3 wasn't mandatory in PAL regions -- this is corroborated by empirical observations elsewhere, like this forum thread from 2004 [3].
The book 'Spatial Audio' [4] by Francis Rumsey mentions that MPEG-2 BC was supposed to be multichannel audio in PAL regions, but this push was later abandoned.
Dolby has lobbied extensively in favor of its own formats. This news article from MIT in 2002 recounts [5] an interesting situation where money exchanged hands between Dolby and MIT after MIT's vote to support Dolby AC-3 in a TV broadcasters consortium's recommendations to the FCC.
[1] http://mpeg.chiariglione.org/content/when-should-i-use-aac-r... [2] https://documentation.apple.com/en/dvdstudiopro/usermanual/i... [3] https://forum.videohelp.com/threads/164582-MPEG-Audio-Vs-LPC... [4] https://books.google.com/books?id=b3kqBgAAQBAJ&pg=PA108&lpg=... [5] http://tech.mit.edu/V122/N54/54hdtv.54n.html
I haven't looked into AC-3, but a lot of audio formats would require a per-item costs or related distribution costs for the data as well. That's one of the reasons why MP3 is annoying to deal with commercially, as it has a cost of 2% of revenue for music broadcast/distribution, or a $2,500 cost to bundle MP3s with a single video game title.