Well, not every Pagespeed feature works with every site. However that tends to get learned the hard way. Those lazy loading images were working a treat on Friday, come monday - ah, no Apple users could see any images, consequently in an instant Pagespeed gets removed.
To take an automotive analogy, Pagespeed is a bit like doing things to a car for improved 'performance'. Let's save weight, let's put some active suspension in there, let's remove a few bits to improve the aero, let's put some 100 octane fuel in the tank and chuck in some twin turbo. All these improvements - let's keep going there are 50 more tweaks we can do in the garage, why not try 38 of them at once? What could possibly go wrong?
So, the main problem with Pagespeed is not how it works it is just that it encourages people to keep going with it, layering on more 'improvements' until the website does the computing equivalent of leaving the road to spontaneously burst into flames.