system
A chat on subreddit /r/NoStupidQuestions
human
Apparition in Harry Potter is a very complex skill, and can often severely injure a wizard if done incorrectly. Additionally, apparition requires a clear mental picture of exactly *where* you want to go, so you can’t apparate somewhere you haven’t been yet. 

The books explain that most wizards in HP don’t bother with apparating if a safer option is readily available, which explains the prevalence of Broomsticks, Floo Powder, Portkeys, and the owl mail system.
gpt
Plus you can’t aparate into Hogwarts so owls are necessary