Also not always true. A previous employer of mine just simply didn't know what sort of offers we could get at that time. I approached the owner of the company (and my boss, small company) with an offer from another company and said "I really don't want to leave, but they reached out to me to start interviewing and sent this offer. I like this place but can't pass up that difference, can we work something out?" And he looked at the offer and said "whoa, I didn't realize this is what other companies pay these days...." Then he beat the offer, and I still got our normal raises at the next review. I left there 2 years later and he told me that he knew I'd leave at some point but wanted to delay it as much as possible.

Some employers, especially small ones, are just completely clueless. Or he lied to me and knew all along but didn't want me to leave so was willing to eat the cost.