The same could be said of OSes using Algol and Mesa. They just hadn't successful startups using them.

There are good reasons that these startups weren't using OSes using Algol and Mesa. You seem to imply that the success of C and Unix is some historical accident as a result of two startups picking Unix randomly, and their choice was bit a function of the technical properties of UNIX and C. Which, is of course, nonsense.

Sun used Unix because Sun was co-founded by Bill Joy. By that time, Joy was already deeply involved in Unix (per BSD). If he didn't find Unix and C likeable and up to the task, they would have made different choices.

SGI and Sun were just one of many catalyzers, like a lot of programming languages have catalyzers.

You just confirmed what I said.

The startups that have chosen UNIX, did so because the owners were part of the American UNIX university culture.

A different background would have mean a very different history in mainstream OSes and their respective system programming languages.

In Europe C had very little meaning until most enterprises started to replace their mainframes by UNIX servers from those companies.