At least around here:
1) Pizza is made on demand, quickly, from a small number of relatively non-perishable, cheap ingredients. You won't throw away a significant dollar value of raw materials. Also, pizza is popular, and your delivery drivers can stay busy. Pizza is so suitable for delivery that it's the ur-example.
2) Indian does have long lead times (the sauce cannot be made on demand), but the core food item is rice (which can be made in advance in bulk, and is also very cheap), and sauce, but the way the restaurant works is they make up a small number of sauce bases, cook up some meat, and then combine when the order is made. You don't necessarily know how much butter chicken will be ordered in a night, but you can cook batches during the night to adjust to demand.
3) Thai, around here, is always run out of an existing successful Thai restaurant, so they can piggy-back off the volume of the restaurant. It also tends to be a bit pricier, probably to reflect the higher margins. It also tends to centre around stir-fry, which again is cooked mostly on demand from a small-ish number of prepared ingredients.
4) Sushi...not popular around here (sushi is, but there is ZERO delivery options), but sandwiches, mexican, and turkish kebabs are. Again, you can get a bunch of cheap bread, tortillas, or pitas, a small number of mostly cheap, mostly non-perishable, mostly interchangable ingredients, and churn out chicken quesadillas, beef burritos, etc. Leftover bread is a small cost, and if you're careful you can minimise loss of meat, as you prepare more batches over the night.
5) Fish and chips (very popular around here), made from frozen ingredients and a VERY small selection of fresh ones, deep friend on demand.
See a pattern? A lot of "combine cheap starch with some fresh vegetables and/or meat that can be prepared quickly, ideally from frozen", where in many cases on-demand labour (putting the sandwich together, putting toppings on the pizza) will be a major chunk of your inputs, and ingredients will be minimal. In all cases you're looking at cuisines where it's relatively popular, the ingredients are relatively cheap, and critically you have a lot of interchangeability, a small number of ingredients, and low preparation times, etc. The fish and chip shop doesn't care if they sell 80 scoops of chips or 40, they've got tons spare in the deep freezer, and they're being cooked on demand; no wastage. Their main concern is just selling enough of anything to cover the cost of the oil in the deep fryer.
What will NOT work is something like a steak, roasts, ribs, fancy fish; stuff that has expensive ingredients and (especially) long lead times. You can't just cook up 40 plates of ribs on spec to see if you'll sell any tonight. (Well, not and stay in business for long.)
And if we look at the screenshot of Munchery's menu, item 1 is Corn Husk Roasted Salmon, item 2 is Honey Glazed Pork, item 3 is a side, item 4 is Roasted Chicken. These are the exact sorts of thing that will wreck your economics. No doubt they were popular; people are sick of pizza, indian, thai, mexican, etc as delivery options, especially at $11 a plate! But as the joke goes, if you lose money on every sale, you can't really make it up in volume. :)
Edit: Munchery tried to work around this by closing orders early, I think at 2pm, but 1) that's going to lose you some volume and 2) that's still not enough lead time.
> why are all pizza, Indian, Thai, Sushi etc. places in my city doing this
They're doing something very different.