And how would you suppose should your client, who wants to use this library on a cRIO-9064 (just to name one of the currently still possible options which are Windows 32-bit, Windows 64-bit, Pharlap ETS, VxWorks, Linux 64-bit, MacOS X 64-bit, Linux ARM) recompile it without having access to the key? Sure with asynchronous encryption you don't have to publish your private key but then you are still again in the same boat! If you want to give a client the possibility to recompile your encrypted VIs (in order to not have to create a precompiled VI for each platform and version your clients may want to use), LabVIEW somehow has to be able to access it on their machine. And if LabVIEW can, someone with enough determination can too.
Sure enough, nowadays LabVIEW could be turned into LabVIEW 365 and you could host your code on your own compile server and only sell a VI referrer to your clients. Anytime a client wants to recompile your VI, he has to contact your compile server, furnish his license number and the desired compile target and everything is easy peasy, unless of course your compile server has a blackout, your internet provider has a service interruption, or you go out of business. All very "nice advantages" of software as a service, rather than a real physical copy.