See the answer I wrote to another question here, since it's highly related.
All GMs have an "opening repertoire" that includes every opening in the game. Some openings, such as the ones that are commonly acknowledged as 'best tries for an opening advantage' they'll know well (e.g. the Ruy Lopez), others they'll not know so well (e.g. the Alekhine defense), but the openings which GMs don't know well are also those that are inferior. More on this later.
When top players prepare for a game, they scrutinize the 'best tries for an opening advantage'. Opponent is much more likely to play these openings for a reason. If opponent plays a fringe opening, then top players fall back on their opening repertoire. They won't be prepared, but they expect that they know enough about the opening to get a playable position anyway - that's why the openings are considered inferior.
So if you play 1. h3, a GM's thought process might look like:
1.h3? I guess all my prep last night is useless now. However, this doesn't put any pressure on me at all. I'll just play as though I am White and opponent got in an extra ...h6 somewhere. What opening is an extra ...h6 not relevant?
And then you end up with e.g. 1. h3 e5 2. e4 Nf6 3. Nc3 Bb4 (3...Bc5 is [slightly] inferior since 4. Nf3 is a reversed Two Knights Defense where Black can't go for 4...Ng4). White's opening is not refuted, but they also have no advantage. Meanwhile, it's not like Black's position is hard to play. If they know how to play the White side of the Ruy Lopez (which GM doesn't), then they can play the Black side of a reverse Ruy as well.
The final question is: is it worth it? You are White, you're supposed to be playing to win, but four moves into the opening you already have no advantage. In return you take opponent out of their preparation, but they still have a position which they know how to play. It's hard to say this is worth it, which is why GMs don't do it either.
If you want to be successful with this, you need a move which takes the opponent out of their comfort zone in a position which you can realistically play for a win - which is what opening preparation is about.