Loading and parsing all those KB of JS for a mobile website is almost a non-starter for publishers, who are now under the gun to shed as much page weight as possible to have a hope at SEO traffic going forward. Also, for people using outer reaches of the mobile web, it can cost up to $50 / GB USD - it seems cruel to cost them $0.05 to use a convenience function. For me, I was working on a serverless node.js function that needed to be able to minimize startup and execution time to control costs. It took a bit of extra work to use js Date, but using Moment literally doubled my cost to run the function.