Because Apple's business is not doing "their own thing". Apple's business is taking something that already is proven to work, and integrate it into something t

Because Apple's business is not doing "their own thing". Apple's business is taking something that already is proven to work, and integrate it into something that makes money. ARM is proven to work. It was designed for phones, tablets, routers, everything. That means you could go to a factory like TSMC and they can reuse in excess of 95% of their hardware chip templates. You can reuse work done in iOS hardware too. We are talking about freaking less than 10 nanometer scale designs!! The transistor's layout at those scales is not even square but calculated with quantum effects with very complex software, and retouched by hand with very expensive feedback using electron and X-rays microscopes. That also means you can reuse the compilers that already exist, the transpilers and the toolchain in general. Hardware designs need literally years of testing in very sophisticated machines(supercomputers) before you use them. Remember that if you make a mistake your entire die is wrong, million of dollars go to the toilet. And you always make mistakes before the design is mature. It is not software that you could update easily and cheaply. If you were to do your own thing , your chips would cost you 100x to 1000x to make just in money. It would also cost you orders of magnitude in time to market. Of course a $trillion company can waste money away(until there is no more money left) but probably they want their money to give profit and create wealth instead of consuming it.