Because that worked so well last time?
Apple's switch to PowerPC which gave them a performance lead over Intel for five years and kept them competitive for another five or Apple's switch to its own ARM Core designs which have given them a 12-24 month performance lead over the entire Android ecosystem?
Bear in mind that Apple dominates the high-end desktop / laptop market, both in market share and profit share* which could put a huge dent in Intel's economies of scale for high end consumer CPUs.
* I'm assuming these figures omit servers. Also, there was a lot of noise in around 2009 saying that Apple had over 90% of the high-end PC market, but I've not seen more recent figures one way or another. Given that PC prices seem to have, if anything, slipped, I doubt it's gotten worse for Apple (and goodness knows the tech press loves any statistic that makes Apple look bad).
The problem with switching to a different architecture is that if it falls behind Intel, people will say "not as fast as a PC." If you stay with Intel and it falls behind, people say nothing. It's risk vs. no reward.