That is a good example of what would get characterized as essential travel.
We have similar in Canada with the USA border and yesterday’s restrictions were for non-essential travel only.
I expect that the definition of essential travel in USA will probably be similar also.
Germany has quite some exceptions by now, due to the fact that there are so many borders and so many people who work in another country or have parts of their everyday life tere, like you can travel for work (that includes athletes), visiting your life partner if he lives in another country, visiting close family, taking care of your animal if it lives in another country (there's a significant amount of people here who have their horse living in another country), ... all those things caused people quite a lot of stress in spring 2020 when borders were really strictly closed. Soem people couldn't see their life partner or parents or horse for like 2 or 3 months. I think it's probably hard to understand for some Australians how tight-knit countries are here. Going to another country here might mean you drive 500 meters and shop in a supermarket in France or Switzerland.
Now due to the mutations, Germany made stricter laws that forbid travelling from "mutation countries" to germany for non-essential reasons nearly completely (that's mainly Brazil, South Africa, Portugal, Great Britain and Ireland). There still are going to be exceptions (they might be a bit stricter), but due to basically all non-essential travel to Germany from those countries not being allowed, a lot of flights will get cancelled and it will make it harder to find travel options. AFAIK Sweden did something similar.
Therefor I think stricter travel restrictions due to countries trying to keep the mutations from spreading are the biggest risk for sports events in March, cause no countries here want to take risks before vaccinations take up speed. I think athletes will usually be allowed to travel anyway (obviously they can even travel to Australia with quarantining or Australian Open wouldn't happen), but the hurdles/quarantine risks might become more annoying and more athletes migth decide it's not worth the effort/risk at the moment.
Nonetheless, I think even Australians travel for not all THAT essential business reasons. The German version of "I'm a celebrity, Get me out of Here" is filmed in Germany this year at the moment, but some Australian guy who commentates on it actually did fly from Australia to Germany only this month to take part in it and I read the Australian authories gave him an exception for that.
I find travelling from Sydney, Australia to Cologne, Germany for taking part in a trashy live tv show not all that much more "essential" than travelling for sports.

, so I think that high horse some people are sitting on is a bit unwarranted for.