Tom hanks caught it in Australia. It's summer there now. Most of the southern hemisphere isn't developed, I don't think they're testing
Improvement due to the seasons isn't simply due to the physiology of the virus itself. People spend less inside and in confined spaces where its easier to contaminate each other. Additionally, the flu does have significant seasonality, and flu season will be tapering off in the coming weeks and months, meaning more healthcare resources to dedicate to coronavirus infections.
It mostly spread through travel, a lot of it business travel. Little spread in less developed countries are likely because of less travel activity.
It may, but improvement regarding weather is related to people staying inside and in very close contact with one another when its cold/winter, nothing to do with temperature killing the virus.
And with fewer pre-existing conditions. People that already have the flu or coughs for other reasons are more likely to need treatment. Late spring or summer usually has empty hospitals and fewer people experiencing a cold, helping with the treatment of Covid