Why look for an alternative before you’re affected in any way?

One reason is to avoid a potential boiling frog scenario. I'm already in one with Android, but there are no viable - for me - alternatives (never touching Apple and mobile Linux isn't there yet) so I'm truly stuck. If there's a chance things may start changing at OpenRouter in such a way that months/years from now I'll look back and say "oh, how I wish I'd switched providers", I'd rather switch now just out of principle than be boiled.

Because its near zero cost now and I can do it calmly. Later, if they start squeezing me I don't want to be doing it under time pressure.

Because it's more likely that not that I will be affected.

There's basically no moat for OpenRouter, you can very easily switch them out to any other of these AI gateway companies.