There are two parts to your comment: "why must students take Algebra" and "most of them will never have to use it".
Algebra can be challenging and difficult to master, but there are many reasons for taking Algebra, the best one being that it gives you the foundation, language, process and methods for problem solving and decision making and for thinking in the abstract.
As far as "most students will never have to use it" - if you can can solve a situation that involves for example, money, time, distance, perimeter or area of an enclosure,or the volume of a container, you are using algebra. If you can calculate miles per gallon and miles per hour, or figure out which cell phone plan is best for you, or adapt a recipe which serves 4 people to serve 10 instead, or set up a spreadsheet to calculate whether to take Social Security at 62 or wait until your full retirement age, given varying rates of return and inflation, thank your Algebra teacher. Those may not be the most complex equations, but you are still solving them using the concepts taught in Algebra.
Here is a good Infographic which highlights the practical uses of subjects
such as history, science, government and math.
For the record, I don't think it's an either-or situation: either teach Algebra or teach practical financial courses. I think there is a need and room for both.
However, I do agree that Johnny often doesn't know about simple financial concepts. Unfortunately in many cases Mom and Dad aren't able to teach Johnny because they don't know them either, and that is sad too.