In a lot of cases, fixing a leak is more expensive than the value of the water being lost, even if it runs into the thousands of gallons. And the drinkable water is not wasted because it ends up back in the system anyway. The cost is to re-sterilise it.
So, people make noise about leaks because they are very visible. (Lots of leaks occur underground and where they can't be seen).
The private sector inherited a nationalised water infrastructure that had seen woeful underinvestment and in Londons case have replaced and repaired thousands of miles worth of pipes. In fact they have reduced leakage far beyond the economic benefit of doing so.
And it may be that they have lost literally tens of thousands of gallons from the Carlton leak, but that is actually fuck all in the grand scheme of how much water that is made drinkable and pumped out through London (and don't forget they take all the shit away too). On a fucking MASSIVE scale. So I can see why this leak isn't really a huge priority.
That said I don't condone them doing nothing and the health and safety aspect when it freezes isn't great. But you need to have some perspective on this. People look at little leaks in front of them rather than the colossal job that Thames Water does for let's face it, about £1 per household per day. I think that's pretty good.