Security is the chief reason in that it's the most important, since AI security is like nuclear waste. But the reason you should use it is it's a standard, and it's better to use one standard and be compatible with 10,000 apps, than have to write 10,000 custom integrations.

When I first used ChatGPT, I thought, "surely someone has written some kind of POP3 or IMAP plugin for ChatGPT so it can just connect to my mail server and download my mail." Nope; you needed to write a ChatGPT-specific integration for mail, which needed to be approved by ChatGPT, etc. Whereas if they supported any remote MCP server, I could just write an MCP server for mail, and have ChatGPT connect to it, ask it to "/search_mail_for_string" or whatever, and poof, You Have Mail(tm).