Dry-cell and rechargeable NiCd/NiMH batteries are in widely-agreed formats (AA, AAA, C, D, 9-volt…).
Li-ion batteries tend to be designed to work in one specific model of one specific product. Then when the company stops supporting that product, it stops making the batteries. The consumer is left with a doorstop or paperweight containing unreclaimable heavy metals and the need to spend X hundred dollars to replace the product, even if it was still perfectly usable and functional.
Standardizing Li-ion batteries would thus reduce waste and lighten the demand on precious metals and other non-renewable resources. (Wouldn’t it? Or am I just dreaming?)