Construction clean-up window cleaning (ccu) is the industry term referring to the removal of paint, caulking, cement, stucco etc. Basically anything that needs more than than soaping up the glass and squeegeeing it.
Typically a window cleaning razor is needed to remove dried paint and other debris from the window.
The process of removing this debris from the window is much more involved than cleaning everyday grime from the window. Window cleaners must charge accordingly.
This video shows what is involved in scraping a window:
As you can see, it is a very time consuming process.
New windows will need CCU. New windows have stickers on them that must be removed. Often there is also plenty of construction debris on new windows as well. Even windows that look like they are free from major debris often have plenty of clear caulking which isn’t very noticeable but which is very stubborn and time consuming to remove.