So the thing on that play is, it's 4th and 3. It's not like a 4th and 12 where a simple 5 yard penalty just gives them 4th down and closer. So there are a whole host of things that can go wrong on 4th and less than 5 by being aggressive -- jumping offsides, running into the kicker, etc...or what happened. Any of which are going to result in a first down and probably kill the game.
As you say, it's really a good outcome on this play to allow the FG, and the odds of something good coming out of being aggressive are too remote and the payoff too low to outweigh the possible risks.
Of course, I don't really expect Walker to be thinking all this in the moment, he's not thinking anything other than he wants to go hard and make a play for his team.
But I do expect his coaching staff to remind the 11 guys out there of what the situation is and advise them to play it safe and take the 3. And so once again, it's on the coaching staff.