Most pen, paper and dice systems share a number of limitations: - TTRPGs need mechanics to fuel immersion, but there is a tangible limit to number of systems GMs and players can keep track of. - Lets face it, no one plays TTRPG to do math and track variables. Aside from being a chore, they can significantly slow down gameplay, especially in more complex systems. - As a partial consequence of previous points, each TTRPG system usually focuses heavily on one mechanic (such as combat in DnD) at the expense of others. There is no easy way to import mechanics from one system to another and each system has a learning curve to overcome. - The truly titanic world crafting efforts of hardcore homebrewers are often enjoyed only by their players. Even if shared online, adopting someone else's ideas into your game requires a lot of effort.