The GitHub website is slow on Safari

Unfortunately this is the fate of most modern sites, they start off simple then they start bloating the website with social media and analytics. SV blokes don't care or notice on their $5k+ top of the line laptops but for everyone else it's an issue

Just microsoft sites.

except it's slow on top of the line laptops, too, so they there's zero excuses

This has all to do with JS devs and everyone converging on this terrible language and ecosystem and nothing with analytics/social media.