A couple of points:
1. In a normal election, you can "vote the bums out" in the next election. This has much more serious and long-term consequences, more akin to a constitutional amendment, which in countries that have a constitution usually requires something like a 2/3rd majority.
2. In a normal election, the side that wins by making promises (false or otherwise) then has to actually deliver on those promises, and be judged on those promises, because it is voted into power. This is not the case here, and in fact the new PM wanted to remain.
3. The lies and false promises in this particular case were quite extreme. Although there probably were some, I can't think of single "leave" promise that was truthful.
4. Yes, you do hear this all the time, but the general idea is that since you can reconsider next time around, the lies should be left to stand and the people voted into power judged by their performance relative to their claims. Again, there is none of that here, as the people behind leave aren't even generally going to be in power, so no judging them against their claims, and this will be hard to undo.
