For you $1300 might not seem like a lot, but for most people, it does matter... Think about the number of DSLR in the current Canon APS-C lineup... 7D, 80D, 77D, T7i, T7, SL2 (and I don't know the lowest model number). People do care about cost and if Canon can sell enough APS_C R-mount cameras, they will.it probably is. I mean here's full frame for 1300 bucks. it'll probably sell for under $1000 before it's gone. what's left is EOS-M
There may be other reasons too which we do not know. While the M series is currently the Mirrorless APS-C, Canon may decide in the future to release an APS-C R camera... RF-S???