Kyrgios has been to Mexico a few times and he's actually a champion of this event. He won in 2019 and when he played the atmosphere was like a soccer match. He referenced that in his tweet calling it some of the best atmospheres he ever played in. The match between Rune and de Minaur started at midnight and it came right after the longest match in tournament history.
Much of the crowd left before a sizebable amoutn returned but these circumstances impacted the poor turnout early on in the match.