C# is the same, int is merely an alias for Int32 and the default Array type only holds 32bit.
If you really need to, it's easy to wrap this into your own BigArray-class holding a 32bit-array-of-32bit-arrays and overriding the []-operator with Int64 as argument.
For comparison, Java's int type is 32 bits on 64 bit systems, but then this limits the array size. It seems like a lesser evil to have a platform-native int type than to limit the size of arrays (especially since servers can be expected to increase their max memory going forward).
Of course, standardizing on 64 bit ints instead would require emulating them on 32 bit systems, when they can't support that much memory anyway (you could argue that 32 bit systems don't matter much anymore, but if you really don't care about ever running on them, then you can just treat 'int' as 64 bits and not variable size).