I don't know how you got that impression, but inside Google people use hash tables far, far more often than B+trees. In fact, I don't think I ever used B+tree

I don't know how you got that impression, but inside Google people use hash tables far, far more often than B+trees. In fact, I don't think I ever used B+tree once in my entire career inside Google. It's pretty hard to beat "expected O(1)".