Schrems II (and the Privacy Shield invalidation) has been in response to the aggressive data collection by the US government, and the extra-territorial nature of legislation used to achieve this. The US is able regain access to the EU market by repealing/changing CLOUD act and similar legislation, so I personally don't think this is (primarily) done to block US companies. However I am not the one implementing these rulings, so the best I can is speculate.

> So is it likely the European Commission did this in an attempt to block US companies from offering internet services to the EU

More like the European Commission did this in an attempt to protect European citizens from having their personal data exfiltrated against their will to the US on order of US law enforcement agencies.

No, EU had an agreement with the US called Privacy shield that allowed US companies to process EU data. However this was struck down by US courts and that is what leaves us with this mess.

If anything, it was a move to push US legislators to respect foreign privacy laws.