Because the option will also be extended to all your colleagues.

And the moment a team gains a single remote worker it gains a load of process and ceremony. Every conversation becomes a scheduled meeting, every scheduled meeting books a meeting room with AV equipment, every meeting gains five minutes of AV setup time, everything that would have been a group of people at a whiteboard turns into a presentation prepared in advance by a single person, and every lightweight task tracking system gets replaced with Jira.

All of which is done with the best of intentions - you don't want Remote Person to be excluded, or unable to see the whiteboard. And the changes aren't terrible - plenty of companies use Jira quite happily. Some people would even prefer a 20 minute scheduled meeting to a 10 minute interruption! But each change makes your life slightly more like the cliches and jokes about corporate life.

It's not all downsides of course; if you get to avoid commuting or working in an open-plan office you might find on balance it's less alienating.