AWS hosts a huge amount of direct Amazon competitors. Explicitly banning certain competitors in an unrelated business would be pretty damaging to the credibility of a platform.
I tried to explain this sort of thing to Intel once about opening up their fabs (before Pat Gelsinger took over as CEO). Selling access to your infrastructure for profit lets you invest in better infrastructure without using profits from the things you sell using that infrastructure internally.
I would say that aws is a rich substrate upon which many businesses can be built - many of which Amazon simply arent interested in getting into. Space ISP is one business and the price/bandwidth ratio is one of the few differentiators and that alone may decide the winner.
So oneweb better get creative about what they’re layering on top of their pipes.