As you found out, changing a company from the inside can be very difficult. James Shore wrote about his experience when he tried to do this and it is a very interesting read.
(It's much easier to change a company as an outside consultant, by the way. I've worked doing that for years now and there are many many "tricks" I use that just don't work if you're an employee. The simplest one? People hired as management consultants get more respect than internal employees, even if the employees know what needs to be done.[1] Sad but true.)
[1] My dad's favorite joke: "A consultant is someone who takes your watch and tells you what time it is. And then keeps the watch."