The wait before the first impression
A page that takes too long to appear loses the guest before the first photo has loaded. That guest rarely returns to find out what was there: the next tab was already open. On the road, on hotel wifi or a patchy train connection, the margin is smaller still.
Speed, in that light, is not a technical detail. It decides whether the visitor is still present at the moment the content arrives. The most carefully chosen photos and the most honest description do nothing for a guest who has already closed the tab.