1) Consumers pay VAT not companies. Companies only collect VAT, unless you mean they are buying goods in the UK.
2) Google use EU cross border services rules to avoid charging VAT in the UK. But since it is b2b it is generally reclaimable so no gain to exchequer either way
3) Uber avoid VAT by classing their drivers as self-employed so they each run a business below the threshold for registration. This is despite being found at fault for this.[0]
So there are some very large cases of US companies not charging VAT.
2) Google use EU cross border services rules to avoid charging VAT in the UK. But since it is b2b it is generally reclaimable so no gain to exchequer either way
3) Uber avoid VAT by classing their drivers as self-employed so they each run a business below the threshold for registration. This is despite being found at fault for this.[0]
So there are some very large cases of US companies not charging VAT.
[0]: https://goodlawproject.org/uber-case/: