A compound of reasons. Wainwright, Suffield and Shilo are good combined arms training ranges which places an armoured brigade in the west (yup, I know, wide separation). An armoured brigade typically has three manoeuvre battalions, at least one of which should be tank heavy. 1 CMBG has four manoeuvre units, LdSH(RC), and 1,2,3 PPCLI. 1 and 2 PPCLI are mech and 3 PPCLI are light. It seems logical to me to retain the LdSH(RC) and 1 and 2 PPCLI and use 3 PPCLI to fill out all the essential positions which are currently unallocated/unmanned in the remaining units.
If you want to see cap badge bias at its ultimate, you should see my org charts for a napkin force of two divisions based on heavy 30/70 use. Only five RegF cap badges survive. RCD, 1 RCR, 1 PPCLI, 1 R22eR, 1 RCHA. Everyone else gets ResF unit names/titles.