The math books that made the list are ones that always rate highly on these lists, but I think they are uniformly bad choices for people with a more passive or recreational interest in math. A lot of textbook publishers have series for undergraduates which are a better choice. For example, here’s Springer’s: https://www.springer.com/series/3423. For someone who has a college level education in science or engineering, but not a math degree, I think they would have more fun looking through a series and picking a title that seems cool and interesting to them. I honestly just have to wonder how many programmers have unread copies of Principles of Mathematical Analysis sitting on their shelves unread.