There could be different reasons.
1. The total number in the Email Link Performance reports adds the number of leads that clicked on each link, i.e. a lead that clicks on two different links in the same email is counted twice. The Clicked metric in the Email Performance Report is a unique count of leads that have clicked on any link, i.e. a lead that clicks on two different links is counted only once.
2. The timeframe filter in the Email Link Performance report is different than the one in the Email Performance report.