I'm speculating, but they might find it more convenient to use a separate device for the video chat? Especially if you're using your laptop a lot during the video call, it's quite convenient to have the chat open elsewhere.
> HIPAA/PIPEDA plans start at $$200 per month per account, which comes with 10 hosts.
Apple's FaceTime is not HIPAA compliant because they haven't filed the paperwork.[1]
(Obviously, there are a lot more steps to it than signing a Business Associate agreement, but I would bet FaceTime is probably a little more secure than Zoom)