From my personal experience, it is a very uncertain and cautious decision to twell your employer about your disability. I knew it would have an impact on my work and that I needed to engage my employer to let them know I needed support. That didn't stop me being cautious and worrying that I may face discrimination or be passed over for promotion. 

I had already disclosed my mental health (depression) when I applied for the job initially, so I had confidence that my employer would support me. My employer has provided all the support I have asked for and I have never been passed over for promotion. Unfortunately, this is unusual in the disability community. Many are discriminated against (despite laws) and are forced out of work.

Against that backdrop, the 4% figure of people disclosing disability is very understandable. Disclo is a new service that allows employers to have employees disclose their disabilities and verify the requests for accommodation. Protecting the employer and employee.  The rise of HR tools and services that make disclosure easier and more confidential will help everyone. The lived experience of Disabled people is key to companies providing products and services for everyone.