These sorts of surveys are often misleading.
You need to know sample size, what groups they asked (like op said if it’s MAS service users it’s not surprising), then you also need to take into account it’s self reporting.
That doesn’t even start to look at why people don’t. Many people don’t because they can’t afford it. CoL has made that worse. Some people are choosing to live like that for other benefits (not talking UC etc), like living on one wage so one parent can be at home. Loads are doing everything they can and can’t get quite on top and are going into debt.
Plenty of people just don’t save and that could have a load of reasons why. When I divorced exh I used the money as a deposit in a small house. I had a small amount in savings left that slowly dwindled away on living expenses. Until 2 years ago I had no savings, due to wage being eaten up by living costs. Exh spent his money on several holidays to places like New York. Took his new girlfriend and her kids away. Took our kids away etc. I know he has nothing left and had bailiffs round. One of the reasons we split is that he spent money faster than it came in. He has also used the MAS or money advice trust, they might be the same thing. It’s his money and up to him about how he uses it. But he could be in a better position but chooses not to. He is living assuming he will get a good chunk of inheritance.
Then take into account the benefit of them doing the survey. If they can prove predict more and more people will need their service they can try and increase their funding. So they aren’t going to ensure it’s completely impartial.