I have to say that I use to work in housekeeping at a hotel when I was 16 years old. I know all the tricks in the book to make a room look clean even when you cut corners.
There are different standards between a occupied room and an unoocupied room. When I worked I would get 15 rooms a day and you would have a max of 1/2 per room. So occuopied rooms you would make the beds, quickly wash the bathroom(getting most of the floor but not all of it) and vacuum the floor.
An occupied room you would clean in more detail, using bleach on the floor, dusting tables and changing the bed sheets, but never the comforter. I have to say I never cleaned the baseboards or bed frames as this was done during spring and fall cleanings, which was also when we cleaned the windows and the curtains. Comforters were only washed once a year.
I have to day that I never use the comforters, unless I know they are changed with each guest.
The full time housekeepers usually are given the same rooms all the time so those who have a sense of ownership, work hard to keep there rooms in good condition, others who are just there to do a job don't. It is really hard to be hired as a housekeeper as not many people want that type of job and burn out is very high.
Most issues from my experience is time. The next is those just trying to get done so they can go home.
These are in no way an excuse for anyone to get a dirty room, but it may help people understand why it happens.
oh crap! 
