At the same time, a lot of people choose an airport hotel either because it's near where their meetings are, or simply to be able to rest right after their flight and deal with getting to their meeting in the morning. The vast majority of people would prefer sleeping in a hotel room over sleeping in a roomette (or even bedroom) on Amtrak - the bed is comfier, there's more room, and you're not feeling the track movement all night (which can be quite rough in some areas!) Add in that coach airfare + an airport hotel is likely cheaper or similarly priced to a roomette on Amtrak, and it's difficult to justify the train for business.
The other wild card with everything is where you need to be for your meeting, visiting family, etc. If you're an employee for US Cellular, for instance, and you need to get to HQ in Chicago, O'Hare is quite a bit closer and more convenient than Union Station downtown (the building is near the Cumberland station.) There's a lot of corporate buildings in the northwest Chicago suburbs as well, and in those cases Amtrak is quite a bit less convenient than flying into O'Hare. The train is very convenient for downtown travel, but if your final destination is at a suburban office park, that "downtown to downtown convenience" isn't so convenient.
There's definitely some market for overnight sleeper travel, and perhaps there's a case for more businesses to use it for business travel, but in Amtrak's current form of doing it I see it staying quite niche. If Amtrak was able to set it up more like a hotel, there might be a bit more room for it on shorter corridors (for example, allow "check-in" from 3 PM - 10 PM where people can get their bags in their room, settle in, and maybe even wind down for the night, travel from 10:30 PM - 6:30 AM, then allow "check-out" from 6:30 AM - 11 AM so people can sleep in, maybe grab breakfast before getting 100% ready, etc.) Even with that, I think it'll be hard for Amtrak to carve out a huge chunk of the market - unless you're going on a single-day trip, you're going to need to be in another hotel anyways, so why not settle in a night early or stay one more night?