'Friend WithEvents' in Visual Basic vs. 'private' in C#

Friend is used for compatibility with older Visual Basic code, where normally a control was used outside the form which contained it.
In C# there isn't that necessity.

private is a better solution, for new code.

Typically VB.NET leans towards exposing too much (privacy is mostly opt-in) whereas C# is the inverse, privacy is typically opt-out. As others have mentioned the reason is likely due to VB.NET's legacy and the "friendliness" of exposing everything; it makes it easy to get started but also leads to poor design and additional effort to ensure loose coupling.

I think it is to help with migration from earlier versions of VB as code in the forms tended to be modified from outside more frequently. Friend is also the default.

Private is better from a code design perspective and is used in C# as there is no similar historic coding practice I guess!