Let's say you're using some random website and want to talk to their sales or support team. How well do you think "download this app to chat with us" is going to go over?
Amazon and Alibaba are pure consumer plays with a mass audience. They deliberately hide the contact forms to force you through self-service UIs.
If you try the same thing with a B2B or other high-touch service, it's not going to end well for you.
Personally I get a terrific amount of value from interacting with my B2B customers through chats, video calls, and screenshares. The customers love it.