Exchange platforms have no real interest in implementing Segwit. Firstly because it's not them who pay the fees, but us, the users. Secondly, they are more focused on growing their company to increase customers number. Updating code can expose the exchanges to vulnerabilities so it's real pressure.
Exchanges have to consolidate every single input at one point, and when you look at what happens with your deposit, it's usually sent back and forth, which all cost them unnecessarily more in fees than when they would have Segwit fully adopted.
If you spend millions in fees every single year as large exchange, which they all really do, then a 30-50% reduction in fees means more net profits without doing much. I think that alone should give an exchange enough incentive to adopt Segwit.
On top of that, being able to offer lower withdrawal fees (especially in times where the fees are shooting up) than competing exchanges is a damn solid way of attracting the mass, because they do care about low withdrawal fees.