Send a Message
Non-voting doesn't send a clear signal to politicians.
One occasional myth is that there is strategic advantage to not voting. "They'll see I didn't vote, and that will send a message." This is, unfortunately, almost never the case.
Not voting is a poor way to send a message, because it's difficult to interpret. Politicians don't know if you didn't vote because they were too centrist or too extreme. You may end up driving them in the opposite direction you intended. Or, they might think you didn’t vote for one of the most common reasons: lack of easy access to voting. Or, they might assume that you read some anti-voting propaganda and are never likely to vote.
There's some clear evidence on this if you look at the 2016 and 2020 Democratic primary races. In 2016, some Bernie Sanders voters stated that if Sanders didn’t win, they wouldn’t vote. "They will fight for my vote next time." Well, in 2020, the Democratic party did not end up nominating Bernie Sanders--the "stay home in 2016" strategy clearly didn't work. In fact, perhaps the opposite strategy worked. Because Bernie Sanders got so much support in 2020, the Biden campaign made extensive outreach efforts to Sanders voters, including making major policy concessions to Sanders.
This short video from the UK points out that even if you go the polls and doodle on your ballot, at least politicians will see that! Whereas if you don't vote you will never be seen in any way: