Houston can free up max contract slot, so they will have other priorities for a while, plus if they sign someone for that money, there will be no more left. Plus they are attempting to sign Sergio Llull from Real Madrid. And they are leaning towards matching Beverley. Plus Lawson is still likely out of Denver, and there are not many suitors with Houston being one of them.
P.S. Up until the draft everyone believed, that Rockets will pick Tyus Jones (PG), whom they reportedly gave a promise to, but they actually went with Dekker, who looks like a natural replacement for Brewer. If promise was real, Houston probably got a commitment from Llull, that he'll come over.