Don't make better the enemy of perfect.
The chips produced still require "packaging" which will be done in Taiwan.
And then the chips will also be assembled into finished products offshore as well.
Once the plant is up and running in Arizona, the business case for the packaging to be done locally will be much stronger.
Apple used to pride itself that they were Made in America but then moved production offshore to cut costs/increase profits.
Now they are just Designed in America.
If you want to bring these processes back to the USA, you have to start somewhere.