It is a retreat because they are not working and creating more problems than they are solving and politicians want to distance themselves from the problems they are causing.
It's a retreat for the second reason. There wasn't anywhere near enough time to ascertain effectiveness - it's been said before on here and other threads that it takes about 6 months for everything to settle down and this is known about with most road schemes, alterations etc.
The council spent no time on framing the issues, engaging with residents, communicating the changes, highlighting the positives and there was no commitment to supporting complementary innovations like Walking Buses (for kids to get to school) or bike share schemes or permitting pop-up businesses in any of the closed areas.
They've squandered money (ironically given to a Tory Council by a Tory Government at the specific behest of Government policy, they've lost whatever goodwill they may have had and they've made it far harder for themselves in trying to change things in future.
Honestly, spineless local Government is the major stumbling block in all of these schemes and plans. It's why things get watered down to be beyond useless as consultation after consultation is ambushed by vocal NIMBYs and the councillors immediately fall over themselves to appease rather than explain. And far from being democracy, it's simply a case of shouting loudest.
The far bigger worry remains that such a poorly executed attempt to make change will impact the longer-term viability of properly addressing the issues as no politician will want to go near it.
Exactly this @Rockets, the council have just blown any possible chances of progression. The anti-LTN side see it as a victory for shouting loudly and protesting, the pro-LTN side haven't had a chance to see any benefits of the scheme, the council have no modelling data worth a damn because it wasn't left in place long enough and the residents (and all the through traffic) see it as carte blanche to just drive anywhere, anytime. What a failure.