Well Starmer had a massive majority and could have got whatever was needed passed to sort out public finances, but his MPs rebelled (or he chickened out).
There isn't that easy a fix. Since Brexit "cake and eat it" lies, and "fuck business" deal (both Boris quotes), business has been a bit well, fucked. Hence high debt, poor economy, seven different prime ministers as people thinking sticking a different person in no 10 will make the screwed trade deals and huge debt magically cease to be.