I'm sure we're all aware that until recently ultimate control of the internet was held by the US government. However, having already ceded that to an independent body that's now just a footnote of history.
Imagine how the US would act if another country (say, Russia or China) were to announce that ICANN is incompetent, and that they are going to take control instead? These countries will feel exactly the same way if the USA were to attempt to take control back now. At best, the result would be the internet fragmenting into two blocks - one run by US, another run by opposing nations. At worst it would be complete fragmentation, with multiple nets each splitting off on their own. Without a single recognised central authority for assigning IP addresses the new authorities would make conflicting decisions on address allocations - global routing would become a thing of the past (oh dear god - please no-one suggest blockchain!).
ICANN at present may be a slow motion car crash, but at least the bystanders are largely left unhurt. By contrast the USA trying to take over would be apocalyptic.