1) When using gear (unlike Alex), you have to repeatedly stop and insert it, referred to as "protection." This slows progress and your partner has to then stop and remove that protection as you ascend. After each pitch (think a rope length), you then have to set up an anchor and organize/sort the gear before progressing. So, using and managing gear takes considerable time.

2) Two climbers are usually taking turns, with one belaying while the other climbs.

3) Alex has a level of competence on rock unmatched by us other climbers; his mastery allows him to swiftly glide through sections where most climbers would need more time to think about the moves, analyze the options, etc.

4) Alex was very familiar with the route, with many sequences memorized. Doing the route with less familiarity is like a puzzle, resulting in slower progress as you figure out how to get through various sections.

5) Alex has better stamina with less need for rest.

6) This is a hard route, and many climbers might fall or rest on their gear repeatedly while working through difficult sections.

I'm sure I'm leaving out a few reasons but in a nutshell, keeping it simple (no gear, no partner, no unknown moves, etc.) increases efficiency.