Outlook data file size

I don’t understand why my outlook .pst file is so large. It was 220 MB, I deleted hundreds of old e-mails from all folders (inbox, sent, drafts) and compacted the file to 130 MB

BUT when I export all my outlook e-mail, contact, tasks and calender to excel files the total data is 500 KB, add to this all the e-mail attachments and the total is less than 5 MB – so how on earth does Outlook end up with a 130 MB file size???