Kanter stays because he is trending upward in a big way, but still doesn't have a trade value that reflects actual value/potential. The best two man lineup for the past month has ironically been Kanter and Favors. Since March 1st, Kanter has averaged something like 14 pts and 10.5 REBs in less than 30 mins. I am pretty sure Jazz are still high on him. Dennis Lindsey basically said he sees Kanter and Gobert as the front court of the future in his interviews earlier this year on 1280.
Hayward will stay because we can't trade him for his value. A sign and trade wouldn't net his full value, and no team would have incentive to do so. Conversely, we have the money to max Hayward for the next 4 years if we wanted to and not have it affect the ability to sign whoever we draft this year. Other teams know this, and will probably see a bidding war as futile. Why would they want to tie up their cap space when they could be recruiting more attainable free agents? Signing Hayward still leaves us with cap space. Letting players walk for cap space, like in the cases of Al and Paul, was a one time thing, and not a message the FO is wanting to send to the league. Forming a habit of letting all of our best players walk at contract time would make us obsolete and non factors in trade talks. Why would any team ever trade with us again if they believed they could just get our players in free agency!?