Some nudie pics or vanilla porn would probably be the least of their worries. I can imagine that a service like imgur spends the bulk of their time cleaning up the nastier bits that inevitably creep their way into such a large site. How many companies really want to inherit a high maintenance mess for such little return? At least with Tumblr and Snapchat you have a strong brand. How many average Internet users outside of Reddit (or the 18-34 male demographic) have even heard of imgur?
Yahoo's purchase of Tumblr and many bids for SnapChat seem to be evidence to the contrary. Cable companies and premium channels also make a lot off of porn.
Porn is fine for large companies as long as they have some cover (the product isn't just porn).