Spamming low crosses is all well and good against Hearts and QPR, but how many low crosses did we have in that run of games against Woolwich, Chelsea, Liverpool Newcastle?
Answer: not many.
That's because in order to hit low crosses you need to get to the byline, and for that you need good build up play, and for that you need a forward line who are good at passing and keeping possession. Which none of the front three in those games were able to do (Werner, Son, Brennan, Richy).
For Celtic it might be enough to have a Kyogo tap-in merchant who touches the ball 5 times per game; that doesn't work in the Prem, where you need all your players contributing.