If this were interpreted by a court or regulator (perhaps as part of an EU anti-trust investigation) as a requirement to have new data automatically exported on an on-going basis, then that is very similar to requiring effectively federation between big services.
They could do whatever they wanted with their customers (pricing, who and how to serve, terms of service, etc.) when they were small enough that users could in practice leave them for a competitor just as easily as they could cut off service.
But if they allowed themselves to grow to into the millions of users, they would have to gradually transition to purely uninvolved, invisible infrastructure, like an underground water pipe. Their users would deal with smaller middlemen instead of the background infrastructure provider. The infrastructure provider would have no way to impose terms of service or philosophical opinions or pricing controls or whatever, which only the middlemen would be allowed, and if the middlemen all conspire, the infrastructure provider wouldn't be able to deny service to a new middleman who offered an alternative.
Basically, the small players deal freely with small players, and the biggest players, instead of gaining leverage, would have to serve them more and control or compete less (or remain small and retain the full freedom of a small player).