There's a lot more risk and responsibility in that. Keeping everything the same from a responsibility standpoint, being closer to his home/alma mater, and doubling salary is plenty of reason.
A head coaching contract would get him a minimum of 5 years and maybe 6. Another DC job gets him a maximum 3 year deal and probably 2. I don't see how a head job is riskier, especially financially. Plus, with a 3rd year in the playoffs, Clemson will probably give him another raise.