I tried dep for a project of mine and could never even get it to the point of doing anything useful. Conversely go mod took about three minutes to migrate to and was super straightforward.
I am very happy that they did not adopt dep, it was in no way ready (and I don't think it was going to significantly improve given more time).
True, there were problems with it, it wasn't perfect by any means.
I guess the main complaint at the time was that it appeared to be "not invented here" syndrome. The community was converging on dep, and then the Go team decided to do something different, for reasons that weren't completely clear. It kinda rammed home the reality that Go is not a community project, it's a Google product controlled by a small team. That definitely has benefits and good points, but it doesn't match everyone's expectations.
I am very happy that they did not adopt dep, it was in no way ready (and I don't think it was going to significantly improve given more time).