The only reason to post an image instead of a pastebin is for engagement. I understand the engagement practices we are subject to on attention marketplaces like twitter, but is it that hard to provide a supplemental pastebin link?
It's not engagement. It's usability. Way better having the image in context than having an external link to a text written with fixed width font. Obviously you should ALSO provide the link to the text in the tweet so one can easily copypaste (if interested in the code/text after seeing the image preview)
Some locations and people have sites like pastebin blocked, but image hosting allowed. Also in case of say technical blog posts, a combination of certain text characters might trigger a false positive for malware on your site. You don't get that problem with images.