If we were willing to spend thirty million on Modric then we would have done it last year, but we didn't. Only Chelsea were interested last year, and Levy put such a high price on Modric they ended up getting Mata instead.
As The Wizard says, the thirty million Hazard money won't be reinvested - it's a special bonus pot to try and sign the really special players that don't come around very often (at most, one per year for all the top clubs in Europe). Sanchez was that player last summer, this summer it's Hazard. Now we'll set it aside and see if another young prodigy makes themselves known next year that we can bid for and lose out on with it