MPs always seemed to have lined their own pockets and many have amassed a small fortune during their terms of office - e.g. Tony Blair, but no doubt there are many others.
Perhaps why Sir Keir has come under so much scrutiny was that his first comments to the cabinet were to set out the standards he expects of his ministrers and that those who failed to meet those standards would face the consequences. Those who live in glasshouses shouldn't throw stones comes to mind.