Is there a law against comfortable chairs at conferences?  

umm...
Because conferences can be boring, and they're designed that way to make sure you don't fall asleep? It's a conspiracy between the hotel managers and the people holding the conference. Make sure our subjects don't get too comfortable and fall asleep during my speech. Hence, uncomfortable chairs 😉

The food and the furniture ca...
The food and the furniture caters to Mr. Lowest Common Denominator, he eats chicken, he doesn't hate beige, he thinks Kenny G in the elevators is kinda relaxing.
I'd like to meet this person, he must be very well catered to, I'd probably want smack him though.

The windows in the rooms...
The windows in the rooms may open an inch if at all...
suicide prevention?
Desks in the room are disasters. The chairs often don't fit, not
adjustable and always the wrong height for computer work.
I always request two queen beds, one for paper work and use it as the desk.
I recall a high school friend picking a career as an interior decorator,
hotels and such. Must be thousands teaching a formula to
18 yr olds with no design sense. Just a career goal.
I'd like to have a word with the hallway carpet people. 🙂

Nowadays I doubt if Marriott, Hilton or
other chain hotels are concerned about comfort and quality when it comes selecting furniture for their conference centers.
Gone are the days of chains hiring interior decorators who would contract with Knoll or Herman Miller to furnish these meeting rooms with quality furnishings.
More likely is they slap together their meetings rooms with Steelcase, HON or other middle-to-lower-end contract furniture companies. Same goes for the healthcare industry. (Check out the lousy furnishings in most hospital and clinic waiting rooms.
I'm not surprised that the Marriott's chairs are not comfortable!

Ouch!
Having just spent 16 hours in a device designed to cause pain that was masquerading as a chair, I have to agree that these things are developed for the hotel's convenience, not a human tush. The horror that I was forced to sit in was a perfect 90 degrees in regards to seat and back and the little clips for the stacking feature drove wedges of anquish into my thighs.
My fellow attendees and I fidgeted so much that the instructor told us all to stand up for 5 mins and stretch about once every 1/2 hour. By the end of the training it was decided that the organization hosting the conference was going to hold back on its payment to the hotel as so much time was lost due to the extreme discomfort of the chairs.
If only the chairs were intelligently designed and affordable...