Why is short-circuiting not the default behavior in VB?

Because the VB team had to maintain backward-compatibility with older code (and programmers!)

If short-circuiting was the default behavior, bitwise operations would get incorrectly interpreted by the compiler.

The Ballad of AndAlso and OrElse by Panopticon Central

Our first thought was that logical operations are much more common than bitwise operations, so we should make And and Or be logical operators and add new bitwise operators named BitAnd, BitOr, BitXor and BitNot (the last two being for completeness). However, during one of the betas it became obvious that this was a pretty bad idea. A VB user who forgets that the new operators exist and uses And when he means BitAnd and Or when he means BitOr would get code that compiles but produces "bad" results.

I do not find short-circuiting to be useful in every case. I use it only when required. For instance, when checking two different and unconnected variables, it would not be required:

  If x > y And y > z Then

  End If

As the article by Paul Vick illustrates (see link provided by Ken Browning above), the perfect scenario in which short-circuiting is useful is when an object has be checked for existence first and then one of its properties is to be evaluated.

  If x IsNot Nothing AndAlso x.Someproperty > 0 Then

  End If

So, in my opinion both syntactical options are very much required.