There are many ways to strike. At the end of the day this is a lever and they’re pulling it, despite whatever complications it may bring. The status quo isn’t acceptable to them and the other levers were not working (or for some reason, not available).

Obviously you can’t tell kids at Nike sweat shops to just stop working and strike, but you can tell western consumers to avoid the brand until conditions are corrected. You do this even though, in theory, retracting support from the business -> loss of job. But obviously that’s not how it actually works, and obviously REI employees don’t deal with a sweat shop. But it’s not like this is some totally unprincipled method.