Comment by phaedrus

It was not (or not just) for cost-saving reasons. It was due to a cross-licensing agreement between Intel and IBM for technology called Bubble Memory which turned out to be flop, but IBM didn't know at the time that it would flop.

"Next came the 8088, the processor for the first IBM PC. Even though IBM engineers at the time wanted to use the Motorola 68000 in the PC, the company already had the rights to produce the 8086 line (by trading rights to Intel for its bubble memory)"

https://www.ibm.com/developerworks/library/pa-microhist/inde...