Because there's absolutely NO reason to. There isn't even an upgraded set of turbos that one can buy that could even begin to utilize the extra flow the cams would provide. The stock turbos can be easily max'ed on the stock cams.
'13 Black Sapphire Metallic 335is DCT, BMS CP/DCI/DPs, MHD E40, Wagner Evo 2
'14 991 GT3, Sapphire Blue / Black, 11.30 @ 124
'07 997TT 6MT, Arctic Silver/Sea Blue: FBO E85, stock turbos: 5.9 60-130 (now with 656 whp, 700 wtq)