Apple mentioned removing PPTP lately, details here
Haven't been able to find in any great detail the "security risks" Apple mentions. I don't mind Shimo VPN as an alternative however for the sake of "security risk" resonating throughout clients running MAC's would like a better answer than the extremely light reasoning Apple brings up. Can't help if the "real" issue is MAC won't support PPTP any longer and rather than just saying so use a play on words regarding security. As well, they never got into L2TP/IPSec and IKEv2/IPSec protocols.