Imgur now blocks several VPNs and have issues loading embedded previews in several fediverse platforms. So instead of using imgur, you could use one of the following alternatives for uploading your images.
https://postimages.org/
https://imgbox.com/
https://imgbb.com/
https://www.imagebam.com/
You can just use fediverse (eg. kbin) to upload your image directly, without any of those instances?
Just because you can, doesn’t mean you should. The individual hosts of the Fediverse are limited on space, and jamming that limited space full of images, rather than using an external image hosting service, is worse for the sustainability of these spaces
In addition, help out your instance admins by resizing the image if you don’t need it in high resolution.
Uploading a 250Kb file rather than a 2.5MB one makes a difference when thousands of users are doing it.
Shouldn’t this be a per instance policy? Why would the onus be on the poster?
Because pretty much all instances are being run by volunteers and hobbyists, and not a for-profit who is profiting from your content. This is just something nice to do for reducing the resources they require to run the service.
Uploading directly uses server resources which are voluntarily provided, that’s why using external providers and just posting links instead is usually better.