Yes, your question is valid.However, large organisations like...

Yes, your question is valid.

However, large organisations like them usually has multiple contractors working for them to mitigate risks, it's not a surprise to see competitors working with same client in that matter. To top that, replacing contracting firm is really really time consuming and cost a lot of $$$, there are only a handful company like Appen,ScaleAI, LionBridge out there that are both reputable and are at large scale.

In the world of IT, it is not common to replace contractor/supplier over another simply because a better pricing/technology for large organisations, there are way too much involved. Not saying it is impossible, but it is extremely difficult and it could take years.