Why would you need a tax? When products are originally designed with an awareness of how people with different abilities will use them there is no extra cost involved. A tax would just incentivize inaccessibility.
I will concede that it does take extra time/money to bolt on accessibility features after a product has been developed. Which is why it can look like companies are being forced/shamed into fixing their inaccessible products. However, when products are put on the market with faulty or broken parts it is completely reasonable and expected that the company that created the product will pay to fix the issues. Inaccessible products are the same as broken products.
I will concede that it does take extra time/money to bolt on accessibility features after a product has been developed. Which is why it can look like companies are being forced/shamed into fixing their inaccessible products. However, when products are put on the market with faulty or broken parts it is completely reasonable and expected that the company that created the product will pay to fix the issues. Inaccessible products are the same as broken products.