Because it fits perfectly with his character. He got the shot at Cena from HHH; and they've established (on RAW) that he's one of HHH's dudes. It opens up tension between Rollins and Owens, and it fits Owens' character (ends justify any and all means).
Also, because no one apparently seems to remember this:
Anyone who demolishes indiscriminately will get cheered sooner rather than later. Brock Lesnar became babyface purely off the fact that he just wrecked everyone's souls. FFS, he ended Taker's streak and still ended up being cheered. Mark Henry started to get cheers during his Hall of Pain run, and that was while he ATTACKED JIM ROSS (which is how long it has been, oof). It feels like folks are trying to cover up the fact they want to cheer for Kevin Owens (regardless of how much of a heel he is) by asking for yet another "dominant ass-kicking heel". Those heels get cheered.
I think the best way to get Owens over as a heel is to have him tease turning babyface in the feud with Cena, and then go all in on being a bully heel with the Authority.