First, players have to agree to have their contracts restructured. They have to be willing to give up money now with the promise that they will get it later. Most players don't want to do that.
Second, Restructuring doesn't give a team more money. It just shifts the amount they owe down the road. Eventually it has to be paid and you are likely to get into a bind with future salary caps. Most teams that restructure believe they are on the cusp of winning a Super Bowl in the next year or two and just need one or two superstar players to get them over the top. Remember that the Chiefs were 2-14 just a year ago. We have too many holes to fill to play accounting games with salaries.