It isn't that PPTP is very good or even at all secure. It is just that it is completely painless to set up and almost universally supported.
L2TP/IPsec by contrast doesn't traverse NATs well, requires several ports open, and is harder to diagnose when things do go wrong (since it can be on different layers).
OpenVPN is likely the best replacement for PPTP, it just still lacks native support on most major platforms (Windows, MacOS, iOS, Android, etc). You need to install a custom client which adds extra friction to getting it setup.
If Microsoft, Apple, and Google all added native OpenVPN support then PPTP would likely die off much faster than it is.
Reddit Discussion: https://www.reddit.com/r/osx/comments/4rwwe5/psa_pptp_vpn_su...
Apple Support Article: https://support.apple.com/en-us/HT206844