We know because we use Democratic Underground and I along with other members (more others than me) have worked to inform everyone about why Uline is bad. Or if we didn't hear it from here we've read it on websites like ProPublica that have reported on Uline's political activities.
The problem is that not everyone does this or even follows politics at all, especially business owners who might be super busy and have very little time to follow politics or any sort much less knowing that Uline supports Trump. Also unfortunately some business owners might even support Trump too.
In the article it explains how he found out:
Reble said he became aware of Ulines support for Trump through an Etee customer.
One of our customers reached out and was like, I love your mission, I love your mandate, I love your products but the boxes you're sending them in make no sense, Reble said.
So it's up to us to inform as many people as possible about why Uline is bad and that they could save money by finding another supplier. If you order something online and it's in a Uline box be sure to contact the supplier and tell them about alternatives. Mention cost savings to motivate even apolitical people to switch.
Heck just think about the fact that there are so many cheaper alternatives to Uline and yet people don't use them because Uline is good at marketing so some people just get the catalogs and order without ever thinking about finding a better price or looking at alternatives.
Another thing to note that the article was from April, 2025 but I saw no one shared it yet but I believe even if you noticed the date your reaction would be equally valid.