Well, for one, the sun here doesn't actually move. For another, there are so many physical processes dependent on it that moving it around would probably be disastrous.

[So strange, and she struggles to understand how the system hasn't collapsed on itself yet.]

Weather control is something quite different, honestly. That's pure physical work. Changing the seasons is magic -- and raising the sun and moon takes something of all three pony gifts to do properly. Before Luna and I took on the jobs, it took a full six of the strongest unicorns to take on the task, and it drained them immensely... but we alicorns actually gain strength from it.