the internet is interconnected.
but ISPS are not centralised under one company all using one DNS

its funny how you start your idea by literally using a plural to describe ISP's and not a singular context.

just because computers are networked together does not make them a single entity controlled by a single point of failure/entity.

the internet has different ISP's in different countries with different policies. if it was all centralised, wouldnt you think russia would have taken out the US 'subsidiary' of your imaginary conglomerate by now