The ollie is a fundamental trick in street skateboarding, and is used to leap onto, over, or off obstacles, or over gaps of unfriendly terrain such as grass or stairs. As so many other tricks depend on it - for example the kickflip and heelflip - the ollie is often the first trick to be learned by a new skateboarder. The ollie typically takes considerable practice to learn.
It looks simple but yet complicated and vice versa. It takes most weeks to months to learn n some even years but a lifetime of effort to be consistent and be perfect at it and able to go higher, faster and further. It is not a feat you achieve once and it can be thrown out of the window if you want to continue to skate well. I've know skateboarders who just does ollies, boned ollies, ollie north and ollie souths, fakie ollies, switch ollies and nollies and nothing else but everytime he's popping them over 3ft height and up ledges, over gaps and down stair sets or over handrails. So no one's gonna argue on that even though he's not bustin some new fangled pressure flip late flip revert or something. He gets mad street creds for those huge ollies.
It is mainly because those items are guaranteed to help you familiarize yourself with the ins and outs of using them. They are a big help in making you feel comfortable when you push off with your feet while also balancing on top of the board when riding. It is not good to go for a very technical product, so it’s best to choose the mentioned types first.