I used to use the lego analogy as part of my explanation about the CMS we used to use when working with clients. It provided you with a box of 30 or so types of assets which when carefully linked together could build the death star, and while the CMS was free you had to pay someone (us) to just how those elements fit together. Pattern Libraries that have too many components make it hard for people to be able to recreate existing site elements, and as Snook points out Tetris might be a better analogy in these cases.
In reality, pattern libraries usually hit an upper limit of around 100 components. Salesforce’s Lightning has 85 components. Shopify’s Polaris has 90. Anything more than that and interfaces become unwieldy. Each component is something that the designer has to design, the developer has to build and maintain, the user has to learn to use.An excerpt from Leggo My Pattern Library Analogy