Basically because those files are open, and so can’t be cleaned - it will get them next time (but may tell you about others that are then open).
The old CCleaner used to do it too - but it didn’t tell you about it, because telling people just confuses them.
Whoever is responsible for the new version isn’t yet experienced enough to realise that and so it now tells and confuses people.
If you prefer the older style CCleaner then for the download link(s) and roll back instructions click this: How to Roll Back from v7 to v6.39 and follow ALL of the instructions there. (If you don’t follow the instructions it will update itself to CCleaner7 again).