Do you have some evidence for that or is it just speculation?
"But more importantly, you can't just count lines of code as if they're all equivalent."
You're right but the Wireguard white paper conclusion claims an advantage for Wireguard based solely upon the lines of code needed to implement.
OpenVPN, Wireguard and IPsec all have their advantages and disadvantages. I have and will use all 3 where appropriate based upon them.
Further, that is not what the WireGuard paper concludes. For instance: the paper makes a note of the fact that WireGuard is designed to be implemented without dynamic memory allocation, which is not a function of lines of code (in fact, it probably adds lines of code).
You do you, but as a practitioner in this space, I'd say using OpenVPN or IPSEC in 2022 without some powerful compatibility, regulatory, or network complexity concern to support it is malpractice. You might disagree, but I think you'd be in the minority of security engineers on the point. Feel free to ask around! The codebases for OpenVPN and the IPSECs are reviled.
The Wireguard paper makes notes of many things including the lines of code needed to implement.
"I'd say using OpenVPN or IPSEC in 2022 without some powerful compatibility, regulatory, or network complexity concern to support it is malpractice."
Life is complicated and those type of concerns are almost always in play which means OpenVPN and IPsec are also always in play. Wireguard is great where it is a fit but there are characteristics of Wireguard which also make it the more complicated and fragile solution in some circumstances.
But more importantly, you can't just count lines of code as if they're all equivalent. There's a trusted core of code that is more important than the rest of the code, and WireGuard's trusted code is microscopic compared to OpenVPN. That's the right word in this case: "microscopic". It's some of the easiest code in the whole kernel to read, even given the cryptography.