My outside view on this: the lawsuit certainly isn't the sole reason why the ACC would have objected to UConn, but I could certainly see lingering feelings playing into it.
Nationwide, I do recall that the lawsuit was perceived to be led by the Connecticut AG, so even though other institutions like Pitt joined in, I can see how some ACC members might still *perceive* that it was a UConn-led lawsuit.
At the same time, UConn was in a position in conference realignment where it really didn't have any margin for error (even though it ought to be in the top 65 or so schools that should be part of a power conference if you were list out who's the most valuable). Syracuse and Pitt have very long histories of football tradition (even if they haven't been that hot recently) while Louisville does have an impressive fan base and facilities for both football and basketball. If UConn was competing with Wake Forest to get into the last spot in the ACC, then they'd likely be in. However, UConn's competition was much stronger than Wake Forest (or Washington State or Baylor or a number of other schools that already have power conference homes). So, if the ACC was comparing Syracuse, Pitt and Louisville to UConn and it was even slightly stuck in the back of people's minds that UConn was the one that led the lawsuit (whether that was actually true or not), then UConn might have been docked some points in an atmosphere where it couldn't afford to lose *any* points.
That might be the biggest takeaway from the past 3 years for UConn and how it ought to approach positioning itself going forward. UConn has a good home market, solid undergrad academics and elite men's and women's basketball, which is what people here obviously want the power conferences to focus upon. However, in this environment when the power conferences really don't have to proactively make any more moves, a school's flaws (whether real or, maybe even more importantly, perceived) are going to be exacerbated and scrutinized. At this point, power conferences can't have any doubts about football tradition. Power conferences can't have any doubts about whether a school is going to turn around and use litigation against them if they don't get their way. Power conferences can't have any doubts about a school's football TV ratings in their home market. A conference like the Big Ten can't have any doubts about a school's AAU status (unless you're named Notre Dame, which is an exception to the general rule in all cases). A conference like the Big 12 can't have any doubts that it's worth it to stretch its league further out in terms of geography. Once again, selling what you have today might look good in comparison to Wake Forest, but you're not competing against Wake Forest for a spot. You're competing against the inertia that says that the power conferences don't need to do anything until all of those grant of rights arrangements expire, which means that your resume has to be flawless (not just good) if you want a prayer of a chance to move before that time (and maybe even if you have to wait until that time).