This discussion on Hacker News has quite a few interesting points about the competing instruction sets and the costs and benefits.
https://news.ycombinator.com/item?id=12300373

Also links within to the operation and economics of chip fabrication.

(The headline is about Intel moving to fabricate some ARM products - presumably because they have lots of capacity and can eke more profit out of having ARM being part of their portfolio: "this announcement is about licensing ARM's physical IP to enable the Intel foundries to fab ARM SoCs for other companies, not about Intel building its own ARM SoCs")

Intel started making ARM based chips in 1998 when they acquired StrongARM from DEC. They sold their XScale business in 2005 but maintained the right to make SoC chips.

So ARM is nothing new to Intel. They have prior form.