I know because it's kind of related to my job. And also it is related to all of your jobs, if you're in the US. They made it harder(more obvious that you're lying) to claim a lot of exemptions. A lot of people claim something crazy like single 9, which really knowing what the 9 means. They also made it less obvious how to claim exempt, for similar reasons.
You can also put in Other Income, which should increase your withholding so you're covered for a 1099 side gig.
Probably for the best, I assume this redesign started in 2015.