His play would have to fall off pretty dramatically to get offers that low. Look at what Marleau got from the Leafs, and Giroux got from the Sens. You‘re looking at 6.5 over 3 years. Maybe he works with them, but anything under 5 is a fantasy.
Giroux and Marleau are / have always been excellent skaters.
Tavares is obviously a fair bit younger than Marleau was, but I think there's probably a greater concern for Tavares' long term projections given how the game continues to get faster and faster, and that his skating has never been spectacular.
Could he get $6m x 3 from a rebuilding team? maybe, but I'm not so sure he wants to do that. I'd imagine that he's looking at contenders only.