as citypw posted it on:

https://lwn.net/Articles/703000/

We don't have such leap of faith in KSPP due to there are several exploitable bugs( CVE-2017-0358, CVE-2016-1583, CVE-2016-0728, CVE-2017-6074, CVE-2017-7184, etc), which can be turned to "massive" exploitations in past couple of months. And it's just the tip of the iceberg in past 16 years:

https://lwn.net/Articles/721122/

There are tons of features from PaX/Grsecurity, e.g: PAGEEXEC/SEGEXEC/ASLR/KERNEXEC/UDEREF/MPROTECT/RAP/etc. None of them are created by KSPP even though some vendors integrated some of features( weakened usually) into hardware in recent years.