Basically, .COM files are not commonly used and definitely not commonly shared on the Internet. The overlap between use cases for .COM files and .com TLDs is almost nothing.

In contrast, .ZIP files are very commonly shared on the Internet as a convenient way to transfer a group of files all at once, and there are a few different techniques for using .ZIP files maliciously. There is a lot more potential for conflicts between .ZIP files and the .zip TLD on the Internet.