gov.uk did not build Universal Jobmatch. gov.uk did not build Universal Jobmatch. Universal Jobmatch is not part of gov.uk. Universal Jobmatch is not part of gov.uk. It is a separate site, operated by separate people, under an entirely separate Government department, which happens to be linked from the gov.uk website.
I'm not entirely sure what part of this isn't getting to you. The DWP is to blame for outsourcing Universal Jobmatch to Monster, gov.uk has absolutely nothing to do with it any more than, say, the passport office does. What you are saying is equivalent to blaming the passport office for Universal Jobmatch - it's crazy, they had nothing to do with it.
If you're angry that Universal Jobmatch exists at all, that's still the DWP's fault, not gov.uk's. gov.uk doesn't get to decide other departments' policies for them, it is in charge of developing digital services to fulfil those policies - and Universal Jobmatch is a legacy system, so gov.uk didn't even do that for the DWP.