I don't think it was a mathematical decision. I mean, I think he understood the math well enough to know that it was very close to a 50/50 choice. It was a true Hobson's choice, in the correct sense of the idiom. It was a choice between two bad alternatives. I think it probably came down to feel, because you could justify either decision on "math".
The odds of converting a fourth and 15 on a 25 yard field and the odds of making a 33 yard field goal can't be measured just on tables. Nor can you do the same with 2 point conversions odds. They have to be decided based on game situation, what matchups you think favor you and whether they favor the possibility of making that conversion, whether you think the game flow makes 16 points an impossibility, whether you think based on what the other team has shown you in the game a 2 point conversion has a decent chance, whether you have enough in your playbook to potentially convert two of them.
You also need to take into account the magnitude of the game, the length of the game, and the potential impact that various score scenarios have on your team and on your opponent. Hearing Belichick and McDaniels after the game, I think they were very focused on the idea of trying to get the game to a one score game, and believing that doing so would give them the best chance to win. Both spoke about how the Falcons had not played under that kind of pressure for the entire game, and both seemed to think that was where they might get an opportunity to make a big play. It seemed clear to me that they were thinking about a turnover. As it turned out, the turnover came early, but the idea that a one-score game might cause some weird decision making actually did turn out partly correct.
In short, I think the math was close enough to a wash to put an experienced coach in position to make the decision based on feel factors, like the end of Super Bowl 49. If it had been a 60/40 decision or something like that then I wouldn't like that kind of analysis, but I think the "math" said "this is a shit spot," and though I will never know what was in his head unless he tells us on this year's version of Do Your Job, my instinct is that the tie breaker for Belichick was that the whole second half he wanted to see what would happen if they could just get it to a one-score game, and kicking the field goal made that a possibility with 9:44 left.
I sincerely hope he would not have made a legitimately suboptimal decision based on the fact that it feels better and more comfortable to have it be a 2 score game. But this was hardly a suboptimal decision. It was close enough to a coin flip to actually apply some coaching and experience to the situation.
Edit: Actually, it wasn't a Hobson's choice! It was actually what people think a Hobson's choice is but isn't.