Maybe because they know more about the domain than you do, and it will take you a lot more back-and-forth with your clanker than it would for them with their clanker.
And maybe they don't, and that's the problem with one-day-old projects: we know for sure that the programmer didn't have time to learn anything from that particular project and we now have to trust them that they know what they are doing. Unfortunately this is wrong in 90+% of the time, so that's kind of a gamble to expect one particular project to tick this box.