Heh. Everytime I post about this, caching is asked about. 
a) we can't cache certain things on the website, because of how we serve our internal ads. I've spent literally dozens and dozens of paid tech hours with my WP developer and a third party to make it work. I'm not spending another dime 
b) we shouldn't HAVE to cache through hoops and whistles just to deal with a defect in how mastodon is structured
This is 1000% a problem with Mastodon, and it's up to the powers that be to fix it. If someone one with 10K+ followers posts a URL for a website, that website gets flooded with thousands and thousands of card requests within milliseconds, often bringing the site to a crawl or a halt. It's so bad, big sites like Youtube, etc no longer serve cards to the fediverse - atleast to the big main servers.