https://historyfacts.com/world-history/article/why-are-historical-doors-so-large/

This article suggests it's as a display of wealth and power, but also for practical reasons like letting in crowds of people.

It also says:

Earlier architecture relied on heavy pivots and iron strap hinges, requiring oversized doors for structural support. But the development of newer materials and designs allowed for more practical, durable doors without the need for excessive size.

It links to another article about door construction back in the day, if you want to learn even more about them.

https://www.buildingconservation.com/articles/early-timber-doors/early-timber-doors.htm