Like so many of those sorts of decisions, Digg leadership ultimately assumed - incorrectly, to be sure - that their users would "get over it" in time.
They'd had minor revolts over the 2.0 and 3.0 redesigns, they'd had sitewide discontent several times during the 3.0 era due to changes in the content algorithm ... Digg had weathered several storms by that point, and I think site management simply assumed they would continue that trend.
There's a perennial issue I think for Authorities in that sort of position where you're exposed to so much baseless griping and complaining from the extremely-vocal minority that you need to gain some ability to filter out negativity and criticism, or you're crippled by it. You cannot make everyone happy and only the unhappy people will bother to express themselves, so you learn to filter out the discontent and focus on the theory, on the goals. Many times you genuinely know better than this or that upset user, and you take solace from that. But from that position, it's so easy to then also block out the more important negative feedback, the necessary criticisms, under the assumption that 'you know better' - because that's how it went the last ten, hundred, thousand, times this sort of thing came up.
Which is IMO a lot of what happened to the whole of Upstairs staff at Reddit. They got so used to users complaining and users being upset about this or that little thing that they had to develop a certain amount of resistance to that feedback - but they've reached a point where they're so resistant to all feedback about their site that they wound up losing touch with the site and its users.
I think a huge part of where Reddit went wrong and will continue to is not having and/or listening to people on staff who are skilled and qualified at simply understanding site users and site user culture. So much of their current issues could have been avoided if they had a person in a leadership position, an equal at the C Suite table, whose whole and total responsibility was understanding the users and speaking 'for' them accurately - representing them as if they're stakeholders in the company.