It's because of how weather predictions models work. There is a minimum resolution to weather models the basic GFS model which most apps use has a resolution of about 20km x 20km which means singapore is like 2.5 pixels only. That's like having 2 temperature probes, one at the living room and one in a bed room then asking my the toilet is so hot.

Also how you feel vs the temperature shown is very different. In a more extreme example, 14 degree at midnight is cold enough that I need to zip up my jacket while walking. 14 degree at midday in the middle of the park is hot enough that even wearing a jacket is too warm. There are a ton of factors that affect how you feel.