If you're not in education many people won't realise is that classroom teachers have directed time. So over the course of the academic year teachers can be directed to teach, be on duty, attend meetings etc for 1265 hours over 195 days. On top of this they have to manage the rest of their workload to ensure they deliver everything required but they can do this at times that suit them. So you can take marking home if necessary or plan lessons.
Promotion to leadership removes the directed time restrictions. Consequently senior staff can be expected to work in school totally unreasonable hours. We have members of SLT arriving before 6am. This pretty much sets the tone for life as SLT. Meetings after school can go on until 7-8pm. Duty in the morning starts at 7.30am. All staff on the leadership scale do both before school, break and lunch duty. They will be expected to staff after school revision classes or support detentions. They're expected to attend and support extracurricular events. The leadership pay starts at £44k and most will still have a significant timetable of classes to teach. So promotion to earn more is really unattractive. The culture in schools and workload is toxic.