Given advancements of computational power an machine learning, how is it still not possible to predict products from chemical reactions?
It's not an all-or-nothing situation, where either we can reliably prediction reaction products, or we have not tried to.  

For instance, drug companies, for many years, have been making extensive use of increasingly powerful, sophisticated, and refined in silico predictive models to choose likely candidates for in vitro testing.  And I would be surprised if they've not also begun to develop, evaluate, and incorporate ML. 

At the same time, these models are not perfect.  So the answer is that it is being done, it's been done for a while, we're getting better and better at it, but we still have a long way to go. 

It will be interesting to see what happens with quantum computing, which is currently in its infancy.