You are very possibly doing nothing wrong; if the task log indicates that the tasks completed successfully (or there is no log entry at all), then Eraser did the job it was supposed to do. But erasing all the free space does not make all deleted files non-recoverable.
Does Recuva display all 218,000 files in its grid when it has completed the scan? That would be a large number for files Recuva thinks might be recoverable, but it would not be a large number of 'files' for Recuva to detect in the initial stages of its scan. What matters is not the number of files Recuva can detect, but the number that it can actually recover, which is a lot smaller. What really matters is the number of files containing sensitive data that can be recovered.
There are a number of threads on this forum which explain why part or whole deleted files reside in apace which is not marked as free. The moral is that security is not a one stop shop; just erasing the free space is not necessarily going to remove all previously deleted sensitive data on your drive, but it's usually a pretty good start. Better yet if you erase files directly; if you do that, they will not be recovered.