Metrorail or to an extent the entire WMATA tends to cater to the 9-5 workers; you can see this with the amount of routes that operate late at night or early in the morning any day of the week. This with the lack of back up options which I mentioned; there are no options of traveling between many stations by bus at all outside of 7-9am and from about 4pm-7pm.
If someone was to audit the system and plot every single bus route and train by the time each run operates you would see, that the system barely works outside of 9-5pm Monday thur Friday.
Anyone that works lets say warehouses, retail, hotels, hospitals (not talking about doctors, but nurses, janitors, signin/checkin staff, security), bars, resturants etc would know. From the comments in the other post about the shutdown seems pretty clear that most of the vistors here work 9-5 jobs and could afford to use Uber everyday if need be.
People are usually at resturants and retail stores anywhere from 2-6 hours before and after they close fixing the places up for business the next day. Now if you think about what time these places close that would be anywhere from 10pm -3am or someone coming in at 3-7am. For somepeople to get off work late night at during those times Metrorail is running hopefully every 20 minutes if there is no track work and buses can be up to every 90 minutes and early in the morning there might not be any service at all.
If you remove the trains in certain places that limits the possiblity of getting workers to these locations at the time they need to. Plus these types of jobs rarely allow you to change your schedule as your work with the needs of the business.