Diversity is a tough sell because in the short term it only adds complexity.
In a context in which all that matters is what you achieved yesterday and what you are going to be doing tomorrow, adding someone to the team that might have different habits, different thoughts, different ideas, a different language, different ways of doing things is only problematic.
What is everybody else going to say? How are they going to adjust? How can we deliver against the targets if most of our time is spent aligning our views? Wouldn’t it be easier to just hire somebody like us, someone we don’t have to explain everything to?
Of course, if your mind is set on the long term, instead, the benefits of diversity are very easy to understand.
What team do you want when everything you have done so far is not going to work anymore (I promise you, it will happen)? How many points of view are you going to consider when that difficult problem nobody can crack is going to be presenting itself once again? What background should your organisation have the next time an interesting new market is going to open up in front of you?
Diversity is always enriching, you just have to give it time. As with most good things, truly.