But it isn't.
A funeral is by its nature a reactive scene. The action - the death - has happened off stage. And because we don't know any of the mourners, we don't really care about their reactions. The grieving widow, the bereft daughter, the relieved son, the grasping nephew...we don't know them so their reactions are a matter of indifference to us.
You can tell us what a great guy the deceased was or what a tyrant, and we're not that interested - they're dead, so we're not going to get to meet them further. Now, it may be that in your careful plan, the deceased IS going to play a major part, but I'm talking about the reader's experience. At the beginning they don't know that because they haven't yet read the rest of your story. They are reacting to what they're reading now without the benefit of being the writer with it all planned out.
Funerals are all about something that has gone. Even the future is framed by the past eg how will I manage without X? The reader wants a promise of what's going to happen in the rest of the novel. They don't want to hang around waiting for the story to start. If you're writing for film or television, you have a small window of opportunity while the viewer decides if they're going to carry on watching (no one walks out of the cinema in the first two minutes, so you've got up to ten minutes to hook them).
But it's different for books. The first thing the reader looks at before parting with their cash and time is the beginning, whether that's in the bookshop or as a downloaded sample. They won't buy if the opening doesn't grab them and funerals, as reactive, not active, scenes don't.
Plus, a lot of people read for entertainment and don't want to read about death and grief. Your novel actually may be a rip roaring romp, but the reader won't know that when they start reading, unless they've been given the book by a friend who gives a quick resume, or have read a lot of positive reviews saying that.
Other bad starts include having the main character waking up or staring at themselves in the mirror thinking about the night before (that's reactive - start with the night before, make it active), and characters setting off on journeys (you're going to have to explain why they go which makes it reactive, so start at the moment when they decide to go, which is active).
There are of course exceptions, and I'm probably going to be deluged with titles of good books that start with funerals. But I'm going to suggest that they work because the funeral itself isn't that important to the characters and the characters aren't reactive, they're active eg they're a gate-crasher or the detective investigating the death. So, Holly Martins turns up at Harry Lime's funeral in The Third Man, because he came to Vienna hoping Harry was going to give him a job. He has to be active, because the job isn't there and then things don't seem to be straight forward about Harry's death and - am I the only one humming the theme tune?
(Cue zither music....)