If the Campaign Tracker section on your Salesforce leads is populated for some leads but not for others, it is likely due to one of these issues:
Please note that you will never get 100% of leads tracked, due to technical issues such as users having Javascript or certain ad blocking extensions in their web browsers. You should get data on 90%+ of web site leads however, which is generally more than enough data to improve your marketing efforts.
best approach is to see if there is any commonality between the leads that are not being tracked. Please contact us if you need assistance.