because play develops. it develops with cassettes too but it's not a huge problem because the force is only one way.

besides, standards don't just happen. companies like level want people to buy their ****, so they make proprietary threadings and bolt patterns. track cogs have had the same threaded interface for many decades, even though better solutions have existed for several years at least.

if a new standard does happen, i'd hope that it'd be bolt on, which is by far the most durable and serviceable. in order for that to happen a big company like shimano or profile will have to start manufacturing cogs and hubs that have a good chainline (bonus if it can be easily respaced for conversion to disc brake use).