Tea has no calories. Es teh manis has 90 because the warung puts about 22g of sugar in the glass, and that is a conservative pour. Some places make it from a jug of pre-sweetened tea, some spoon sugar into the glass, and the ones that use syrup or three heaped spoons are closer to 150. A glass of es teh tawar (unsweetened) is 2 calories. Same tea, same ice, 88 calories apart.
The problem is frequency, not the glass. Es teh manis is Rp 3,000 to 5,000 and it comes with lunch, then with the afternoon gorengan, then with dinner. Three glasses a day is 270 calories of sugar, and over a month that is 8,000 calories, roughly a kilo of fat, from something that does not register as food. Nobody remembers drinking it.
The jumbo cups are a different thing. The Rp 5,000 to 8,000 'es teh jumbo' stands with the 500ml cup are 200 calories each, and the flavoured ones with lychee or lemon syrup are 250. Bottled sweet tea is in the same range: a 450ml bottle is around 160 to 180 calories depending on the brand, which is about the same sugar as a can of cola.
For comparison, teh tarik in Malaysia is about 130 because of the condensed milk, and a teh botol is about 90 per 350ml. Es teh manis is not the worst drink on the menu. It is just the one you have most often.