Technically 90 seconds is an order of magnitude more difficult than making a regular link. Not a huge hurdle, but I don't need to read any docs or go fetch embed code to make a link.
... I guess it's also because I'm using Rails, so I'm already generating links via a helper function. So I wrote another, one line helper that does the wrapping. So that initial 90 seconds is amortized over every new Like button I add, because I use like_url rather than link_to.
Also, often like buttons are used on something like stories, so you're only adding the code to one template, and now you have tons of like buttons all over.
It took me approximately 90 seconds to implement from looking at the docs to deploy to one of my sites.