I've just demolished a couple of Lidl's caramel wafer bars before I go to work - just like Tunnock's ones but a third cheaper. Anyway, back to gearing.....
Big advantage of a triple for hills is the gear ratios are very closely spaced. For example on my Raleigh Pioneer, the small front ring is 28T and I've got 28T, 24T, 21T, 18T, 16T, and 14T sprockets on the back.
There's a stretch of road I ride with a variable steepness uphill gradient which has more than one set of traffic lights en route so it's nice to have a low gear for pulling away in.
At one point, I will generally use 28T/24T to move off in. Then, according to how the road is flattening or steepening, I will use either 28T/24T, 28T/21T or 28T/18T, which are 32", 36", and 42" gears. The closeness of the ratios means I don't bust a gut getting up the road and I remain in the saddle.
A 1x transmission simply doesn't give you so many closely spaced low gears unless you fit a small front chainring and constrain yourself to a low top gear. A triple is more flexible and the chainring wear isn't all concentrated on one ring if you use the appropriate front ring for the general terrain and wind direction.