Where did you get the idea that discrimination has to be the result of an active effort? Anything that makes one group of people excluded or treated worse is discrimination, even if it is the result of an oversight.
Your second sentence is basically exactly the problem: able-bodied people are arbitrarily treated as the “default”, and others are left out.
Your second sentence is basically exactly the problem: able-bodied people are arbitrarily treated as the “default”, and others are left out.