Since 2016, it has been possible to practice on the grass courts in Mallorca. There were no grass courts in Mallorca before 2016. The Santa Ponsa tennis club (80 km/50 miles away from Manacor, Rafa's hometown) opened their new grass courts in spring 2016 and hosted Spain’s first grass court tournament, the WTA Mallorca Open, in June. Rafa was supposed to practice on the new grass courts in 2016, but due to his wrist injury he only visited the venue. He practiced there in 2017 & 2018. The WTA tournament officials expect Rafa to practice at the Santa Ponsa tennis club also this year [Source: the tournament FB]. Toni Nadal has been the tournament director of the WTA Mallorca Open since 2016.
And he can control the amount of rest he has and the pacing and spacing of his training.
Playing Halle or Queens was nothing but trouble, plus an early loss at those events can hurt Rafa's confidence, especially if its a beatdown by Dustin Brown
But of course the money was a lure, plus he won Queens (beating Bjorkman, Nishikori, Karlovic, Roddick and Djokovic) and Wimbledon 2008, so I can understand why his team considered it a good idea at first.