It's more likely ignorance of your specific market price than malice.
First, the employer isn't even going to know your outside market price if you don't get an offer in the first place. For you to prove that you're worth the 10% salary increase, you would have to be vetted by a prospective employer as having met their requirements to be hired at some price.
Secondly, your current employer needs to agree that you're worth that 10% salary increase. Their perception of your value may simply not match your own perception of your value.