According to the documentation,
"Data to distribute among bins, specified as a vector, matrix, or multidimensional array. If X is not a vector, then histcounts treats it as a single column vector, X(:)."
So, you are out of luck hoping to avoid a loop over several vectors.
Already, your bit of code is certainly much shorter than, say, the code for the histcounts function itself, which hides all the complexity of the histogram algorithm.
If you don't want to see the for loop, then I suggest you take a similar approach. Embed the for loop in a function of your own -- maybe call it histcountsMatrix, and then just call the function as a one-liner.