You seem confidant in your ability to present your exact needs and understand the product and so on, that's good, you're probably right.
But when it comes to something complex, something someone hasn't used before, and all the options and dynamics between enterprise departments that might not be pulling in the same direction, an email almost never covers it and often enterprises aren't aware of it to put it in an email.
If you don't address / discover those things it is potentially a recipient for disaster for everyone.
I've been on numerous calls where a potential customer is on the call and even asking about basic features, then one department head explains to the other "Well we can't do that because X,Y,Z and our other systems A,B,C." and it's the first those two departments REALLY heard each other talk about that. Then we find ways to sort it out.
I've even been on calls where for most of it I'm just there, not doing anything, it's the customer discovering their own processes and working it out internally.
In email that's almost always "we can't do that" because of course not, they're alone with their email, nobody is explaining or offering solutions.
Right or wrong it's just human nature and email doesn't work for some things.