It's only a problem at a really large scale. At the scale of Microsoft or Facebook, there are factors that lead to the use of a monorepo being more efficient. At that big of a scale, companies have enough resource to develop internal tooling to deal with the problem (e.g. the use of Mercurial at Facebook).
FWIW, in case of Microsoft at least, it's more a question of product size than company size. Microsoft doesn't use a single monorepo for everything, like Google (so far as I know) does - just look at http://github.com/microsoft/; and that's not even counting all the VSO repos! It uses product-specific monorepos for some large products.
It would be nice if you and everyone else stopped gatekeeping this problem.
We have 600 devs and face these problems. I can assure you we sure as hell dont have the resources spare to reroll git. We're way too busy rerolling everything else.
