Why don't desk chairs have seat belts?
Because unlike in cars there isn't much chair accidents? ;)
More seriously, no seat belt can help you sit correctly in a chair. What can help you, easily and cheaply, is sitting less. Regularly make breaks and get up, move do stuff that you can do standing up. This one is not cheap but using one of those sit/stand desks can help in that regard — I consider mine the second best health spending I ever made, the first one being: good walking shoes (another great habit for one's health is to walk as much and as regularly as one can).
Not the few communities I follow. Also I only read my Subscribed timeline.
I would love for a way to only see pictures if I click them, though.