The batteries in a Leaf are a significant fraction of the price, few business want to spend $120k on batteries, when they can get them for 'free' from their workers.
The cost of the batteries is small in comparison to maintenance. Managing the batteries means hiring someone with that knowledge or paying for training/other development to get it in-house...at which point, those people would become more desirable on the job market as more buildings installed battery systems, increasing cost of retaining that talent. Then there are the business processes that need to be developed, the provisioning of a room to store them (and OSHA/building code concerns around a room full of batteries, which is no minor thing), and so on.
Or, they can just use the cars parked outside, offloading all of that effort to the owners of the cars.
When the company sanctions plugging into the companies grid, the maintenance and potential OSHA violations that go along with the cars is now their responsibility as well.
The company ends up with more responsibility, not less, because now they have to make sure your car isn't going to be any more of a risk since its powering the building