It had little to do with the contract size. Starlink was being investigated to determine how the Russians were getting/using them.

https://www.newsweek.com/usaid-elon-musk-starlink-probe-ukra...

This raises a potential conflict of interest, as Musk's company was under investigation by USAID shortly before he began calling for the shutdown. Starlink's activity in Eastern Europe has been criticized, with many Russian operatives claiming to have access to Starlink despite Musk's assurances that only Ukraine was using the service.

Additionally, in September last year, Ukrainian forces downed a Russian drone that had a Starlink terminal integrated with its systems, raising questions as to how secure Starlink's operations during the Ukraine war are.

USAID has no ability to investigate or enforce sanctions, so that doesn’t make sense.