Well, I have a couple of reasons.
Security-wise both are similars, IKE/IPsec encryption has no major known vulnerabilities, and properly implemented he still secure and easy to manage, without Radius or certificates. L2TP/IPSEC also do this things, but NAT traversal (NAT-T) is more problematic due to the common use of ESP in transport mode. I have already figure issues to connect with some telecom providers.
The second reason, is more emotional. Since many years, I use Cisco IPsec client at office, with Windows platform. Last week when I seen that PPTP was removed, my fist idea was to replace my personal VPN with IKE/IPsec.