that's because philosophy is a conversation, a dialogism, you don't interpret the world by yourself, you talk with others and come up with a conclusion that suits your vision best, and then once it's done, someone of your acabit will have a look into your work and build his own idea of the world based on yours, and try to overcome the initial postulate by reusing some arguments to better contradicting the others.

You can't understand anything in philosophy if you don't oppose ideas between connected peoples. For example, I'm french so I'll use this philosopher: You can't properly understand Descartes, if you don't read Montaigne, because the latter describes a world that Descartes reus afterward, and following this, if you really want to comprehend his work, you'd have to read D. Hume, because he's the actual direct opposition to rationalism in a direct response to R. Descartes, so reading him allows 2 things : being able to follow the flow of ideas and build a mindset that allows you to have an actual grasp to philosophy in the regard of the chronology, and secondly, it makes you able to come back better to understand what their predecessor thought, because these people had an interpretation on it that is probably the most accurate you'll get.

It's also why philosophy is easy to get into, and very hard to dig in deeper. It's easier to focus on one author and using it as a referential, than intercrossing them juxtaposingly and developping an actual "philosophical identity" that is essentially yours.