Simply put, when you level up you are presented with choices and they are simplified to make leveling quick and keep you in the action. This is in contrast to passive level ups, for example, which apply to you or your items without any interaction. In survivors-likes you are often presented with 3-4 options, making it quick to choose and continue playing your run while offering a lot of randomization. This is also somewhat in contrast to ARPG style skill trees – level choices are generally presented without being able to see the other skill trees. You have to pick and go with it. Sometimes these games pick simple UI over showing you all the stats and some players prefer this.