It's obvious why you don't understand. You use voice chat and are fully capable of using voice chat and, you refuse to look past how you feel about it.
Your line of thinking is what proves it. "The point of voice chat is cohesion ,not to exclude someone" you say, then go on to say "whats the point of push to talk if you're going to have to type it out"
If you don't want to exclude anyone you make sure your team is on the same page regardless of whether they chose to be on TS or not, if that means typing out something you just said then you do so. That's what makes a good team. Willing to do things to help everyone succeed without pushing them.
In your line of thinking. What's the point in me calling out Petrifaction. Can you not read the cast bar that says Petrifaction is casting? Why do you need me to tell you to turn around every single time? You are privy to the exact same information I am on my screen.
It's all about what you're comfortable with, some people love voice chat. Some people can't do it. If you really want to succeed as a raid group, and as a real team, you have to learn to give leeway to people to help them feel comfortable. If someone is anxious the whole time during a raid because they're on voice chat , that becomes a problem. If it means you have to type out a couple of things, then you're going to have to sacrifice those few moments it takes to answer a couple of questions for the success of the group as a whole.
You ask the question of why should you have to type it to them?
I ask the question of ,why I should have to call out a mechanic that everyone can see if they're paying attention.
Voice chat isn't the end all be all. You just assume it is because you make use of it.
You want to be a good team and there's an amazing player that can't use voice chat? You either take the player, or you can try to find someone else who does use voice chat. But if you turn down that player for a worse one, what did you accomplish in progression for your group? Did you really do everything you could ? Or did you just do what is more "comfortable for you" because using voice is comfortable to you.
Well guess what? When they told you No to using teamspeak? They also did what was more comfortable for them by telling you they refuse.
Someone has to compromise somewhere. And me personally? I'd rather type out things to a good /fun /nice player, then callout things to a bad/toxic/ or a player who isn't willing to learn.
You can either learn to compromise or you don't. But don't assume that any of this has to do with VOIP.
VOIP is just a tool. The person using the tool is the one determining the way its used. Thus any exclusion is in fault of our community. That makes it a community problem.