I'll give you a better answer, my dear friend. At first, I had the same doubt, and back then, I pretended to understand the topic, but in reality, I couldn't explain the difference, for example. First, you need to know that these are two different things. VanitySearch uses normal brute force (it tests every combination until it finds the answer = cracks the private key). On the other hand, Kangaroo is an algorithm used to crack private keys when the corresponding public key is known. Kangaroo uses "mathematical techniques" to exploit this, instead of testing combination by combination.

Let me create an analogy: Imagine you're in a forest looking for a specific tree, but the size of this forest is very large, enormous, gigantic, and you have two strategies to find this tree: 

-- You could choose to walk randomly through the forest, checking every tree you encounter until you find the specific one. This approach has no specific direction and relies heavily on luck to find the right tree. You could even be the fastest person in the world, but in such a vast forest, this could take years because you're trying all possibilities without an optimized plan (VanitySearch). 

-- Now imagine you have a map of the forest with predefined trails that increase the chances of finding that tree. The "kangaroo" jumps between strategic points along these intelligent trails, significantly reducing the time needed to reach the desired tree. Even though each jump may be slower compared to VanitySearch, this optimized strategy allows you to find the specific tree much faster by taking advantage of the mathematical algorithm created by a super-intelligent guy named John M. Pollard (Pollard's Kangaroo)