Gusev crater is a former outflow region at the base of the Eridania basin (marked with the black contour in the image below).
This region has recieved renewed attention and interest recently, after new findings were published highlighting possible hydrothermal seafloor deposits (black shading inside white contours).
I'm just speculating here, but that might play a role in the continued interest in that region. The website you've linked mentions "The discovery that hot springs flowed here" and "past floods that may have formed a shallow lake in Gusev".
As far as I remember the literature, it is consensus at the moment that Gusev crater didn't have any standing bodies of water. If it had only transient water content, then that would provide an oppurtunity to study both dry and wet environments near each other.
This is of course something you want to do, if you send an expensive rover to another planet.
After digging a little bit more, it seems that the final three candidates were decided on in a workshop earlier in 2017. In the recommendation letter to Mars exploration lead scientist the results of the vote on assessment of potential scientific merit are documented for all the 8 competing sites.
As one sees there, Columbia hills was voted relatively high up compared to other sites, but shares a close 3rd rank with 3 other sites. Especially in the criteria "astrobiological relevance" and "possibility that stored samples there lead to new breakthroughs" Columbia Hills ranked pretty low. Eberswalde crater and Mawrath vallis even had consistently higher rating than Columbia, but where not selected.
If you then look at the time schedule of the workshop, one sees that the Columbia Hills area was pretty overrepresented in terms of numbers of "speakers pro-Columbia".
This must of course be a bias stemming from the number of publications and the work being done based on the Spirit rover.
So in spite of having many speakers speaking out in favor of the Columbia Hills, it got only a shaky 3rd rank in the total evaluation.
In total it seems for me that Gusev and the Columbia Hills will not be visited again, but there was a strong push to go there again based on previous work.
I will not say that this looks like group inertia to me, because I didn't look through any of the 7 pro-Columbia presentations. But if anybody else is willing to do this, go ahead.