This is probably an extension of their hostility to mp3s. They wanted to force people away from downloaded or ripped content and toward their own store.
That is ahistoric. Apple was forced into FairPlay by the labels, not by choice. They moved to non-DRM'd M4P as soon the labels let them.
As for why they preferred M4P (AAC) to MP3, it was a licensing issue. MP3 was patent encumbered until 2017. Apple, being Apple, didn't want to pay to license the encoder I believe.
> However, a patent license is required for all manufacturers or developers of AAC "end-user" codecs.[52] The terms (as disclosed to SEC) uses per-unit pricing. In the case of software, each computer running the software is to be considered a separate "unit".[53]
[…]
> The AAC patent holders include Bell Labs, Dolby, ETRI, Fraunhofer, JVC Kenwood, LG Electronics, Microsoft, NEC, NTT (and its subsidiary NTT Docomo), Panasonic, Philips, and Sony Corporation.[16][1] Based on the list of patents from the SEC terms, the last baseline AAC patent expires in 2028, and the last patent for all AAC extensions mentioned expires in 2031.[57]
Yes, AAC is also patent encumbered, but the structure of the fees was apparently "better" for Apple. This was heavily discussed … Jesus, 15 years ago now … when everyone was pissed Apple didn't use MP3s.
Basically, AAC was cheaper for Apple so that's what they used.
But AAC was as "open" as MP3 and there was never any "lock in".
Small correction although you’re mostly right: m4p is the FairPlay encumbered file extension and unencumbered AAC audio files are (by default in iTunes) m4a.
> This is probably an extension of their hostility to mp3s.
Apple was never "hostile to MP3". Even iTunes 1.0 (considered an "MP3 player" back then) supported ripping CDs to MP3, using the Fraunhofer MP3 encoder that was far superior to alternatives (especially at that time).
As for why they preferred M4P (AAC) to MP3, it was a licensing issue. MP3 was patent encumbered until 2017. Apple, being Apple, didn't want to pay to license the encoder I believe.