LOL, thats the problem with making assumptions, often they will be wrong

. To further your education the EF/EFS to EFM adaptor is nothing more than a spacer with electrical contacts running through it, no fancy software or anything, just a spacer.
Wow, has the penny finally dropped

. Yes all but a few very early EF mount lenses work natively on the EOS-M cameras with the spacer/adaptor. Some of the early lenses dont play well with the DPAF focussing system wether that is on a DSLR or Mirrorless. Oh and as well as making assumptions, you cant count either, 2012 was only 6 years ago
Far from it, Canon have even included an adaptor with the additional control ring that is on the R mount lenses so that the EF/EFS lenses will have the same functionality.
They could have kept the same mount, but wanted to include extra functions in the lenses and to open new possibilities in lens design, so went for a new mount with additional contacts.
Hope this helps you understand a bit more about the new introductions.