For instance it means leaving the browser and have the default email client handling it. For some people it becomes a distraction, for other they didn't even setup the default client so it's a setup screen and hey have to copy/paste the email to their gmail tab.

Other people actually don't want to give their email but will give a phone number, or their Twitter handle, a chat ID, or their address, or anything else really.

A form is more maintenance, but can be pretty beneficial to address a general public.