Before they went to Intel, they were at the mercy of Motorola, which couldn't keep up with Intel.
The problem Apple had with IBM was that IBM didn't care enough about power efficiency to make the chips viable in laptops. They also weren't that interested in fast iterations of incremental improvements.
When the G4 first game out, it was far, far ahead of x86. Apple offered it at 350, 400 and 450 MHz but shipped maybe a few hundred or a few thousand at 450 MHz and a few tens of thousands at 400 MHz. Those computers blew the Pentium out of the water. Intel eventually caught up and passed them purely on manufacturing ability.
Then the G5 came out, which was a beast of a processor. But it never came out for mobile, and IBM only upgraded the speed once or twice before Apple went for Intel.