Why aren't teams offer sheeting him?
Why would they? Speculation is that Tkachuk is mostly interested in a bridge deal, so what would be the point of offering him 3 years, 7M per or whatever? Ottawa would just match.
A 4 year offer sheet might put Ottawa in a bit of a bind as I doubt they want to walk him straight to UFA status, but they would still match and then just trade him 3 years down the road.
Then you have to consider what teams even have the picks to do it - Arizona, Buffalo, Dallas, Detroit, Minnesota, Montreal, Nashville, New Jersey and Seattle. Some of those teams are not going to want to punt off a high 1st or 2, and some don't have the cap space. I guess Carolina could do it if they don't get Kotkaniemi.