You lose dependency on a monolithic library which creates vertically-stacking dependencies and library conflicts. By ditching it, you gain the ability to construct your app out of loosely-bound components supported by independent developers.
Obviously, you cannot have dependency conflicts if you only have a single dependency! We need a slightly more complicated example to understand the problem. Let's say I'm making the new customer checkout page for my startup.
I decide to call an e-mail address verification as a service API, their library uses jquery 1.8
I decide to call an address verification as a service API, their library uses jquery 1.11
I decide to call a credit card validation as a service API, their library uses jquery 2.0
You go to the e-mail address verification company and say "Do you have a version that supports a newer version of jquery" and they say "yes, also we redesigned our library's interface so if you upgrade you'll have to change all your code..."
