There are many explanations for this:
- Not all clicks necessarily go to a landing page so you may have many more clicks than landing page visits
- More likely, it is concerning a link scanner that is "clicking" the link in the email but not necessarily "visiting" the landing page. These fake "clicks" deliver false positives and Marketo logs this activity as if the person themselves clicked the link in the email. More info here: Email was clicked before it was delivered? It's a link scanner
Devraj Grewal is right - I would look at an email link report for the email(s) of concern, and check how many clicks are actually to the landing page URL. If the disparity is still significant, conduct some checks to see whether link scanners are to blame.