Follow the sun does not happen by itself. Very few if any engineering teams are equally split across thirds of the globe in such a way that (say) Asia can cover if both EMEA and the Americas are offline.

Having two sites cover the pager is common, but even then you only have 16 working hours at best and somebody has to take the pager early/late.

Not to mention that the knowledge, skills, experience to troubleshoot/recover is rarely evenly distributed across the teams.