Running a Tor relay is too hard and complicated for many people who may want to help Tor.
Why there is no click-to-run method for running a Tor relay?
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Especially for Windows users
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The short answer is that it could be. It is open source and anyone can write their own tool that could automate a one-click solution.
The longer answer is because Tor isn't simple. The truth is that making an "easy" button is actually kind of a bad idea. A good relay operator is a well-informed relay operator. That means spending time learning the things that make Tor hard and complicated. There are lots of tutorials out there that will take you through the process. Here is the Tor Relay Guide and here is the information on joining the Relay operator mailing list.
If you would like to help fellow Tor users in countries where the internet is heavily censored but don't have the time to dedicate to setting up a relay, check out Project Snowflake.