That's because of a number of reasons, mainly the 'Napster' effect of the majority of files being .mp3. i.e. back in the days of dialup internet and small hard drive capacities and the start of mass p2p with Napster, mp3 was the only real viable lossy codec for compressed audio / small file size (Vorbis didn't exist, nor did others like MPC, AAC was in it's infancy). If companies could choose, they would choose AAC because of no licensing fees and also it's the new industry standard as it's included and part of the latest MPEG standardisation, that being MPEG-4. If mp3 were still the preferred industry standard, it would be part of the MPEG-4 container standard but it isn't. yes, both are industry standard but however what's the new industry standard......
mp3 is an outdated codec in many ways. It was replaced in the MPEG-2 standard gees.....
AAC and Vorbis are more accurate, more flexible, and compresses better than mp3. ~192kbps AAC and Vorbis (both are natively VBR) is more accurate and represents more data than 320 kbps CBR / VBR -V0 mp3. Easily proven objectively via spectrograms you can do in 5 minutes. AAC is better than Vorbis tbh (lots of reasons from accuracy to power consumption). Both however are significantly better than mp3.
FLAC and AAC are both the leading codecs for lossless and lossy respectively for overall codec quality objectively. Other codecs are better at some aspects than both, but in terms of overall, both triumph over the rest.