I think that most travelers learn a surprising and slightly painful lesson on their first visit to Europe: old things - including the iconic monuments you have dreamed of seeing on your trip - need maintenance, and sometime the very things that you have traveled so far to see are closed or covered up with scaffolding and a tarp. It's part of the bargain. You get to see amazing, wonderful, things. A few of them (hopefully just a few) may be partially or fully covered. This happens to everyone. You are full of anticipation, excited to see that famous thing, you come closer, you sense the moment you have been waiting for is near, you turn a corner, and there it is, in all it's glory, and, and....oh, awwww. It's being renovated. : (
I try to just shrug, chuckle a little bit at myself, and make the best of it. Sometimes you get that picture you had been hoping for, sometimes you buy the post card.
Hopefully by the time we can all travel again (whenever that will be) the pictures will show Big Ben without any scaffolding or covering tarps.