The GitHub website is slow on Safari

Well yeah, but just imagine how much money they’re saving by delivering a subpar experience!

Or how much money they are capturing in investiments or corporate deals because of the tech stack

They're not even saving any money. Syntax highlighting is a trivial workload, whereas the average SPA spends a lot of time in pointless roundtrips that have the server send more data down the pipe than the SSR equivalent.

I guess if you say "we've made the UX worse" instead of "we've reduced costs but made the UX worse" to shareholders, they think of cost savings regardless.

I'll play devils advocate - does it save them some storage space or bandwidth in the CDN that delivers Github?

That's a good question, without looking into any of the code id say bandwidth cost goes higher when moving away from server side rendering since you have to send the code for client side rending to each client which connects.

Sending data is what’s trivial compared to compute… syntax highlighting is not trivial workload compared to that, you don’t know what you’re saying.

You say that, until you’re one of the unlucky people who discover that cloud DBs are just cloud VMs in disguise, and those cloud VMs have network throughput limits.

A fun part of a retro at my company last year was me explaining to a team, “had all of your pods’ requests succeeded, the DB would have been pushing out well over 200 Gbps, which is generally reserved for top-of-rack switches.” Of course, someone else then had to translate that into “4K Blu-Rays per second,” because web devs aren’t typically familiar with networking, racks, data centers…

Serving static files off highly efficient, distributed CDNs is a solved problem. There's no "4K blu-rays per second" when you're talking about gzipped, highly cacheable text data.

If github has a million users visiting it per day on a FRESH cache, and all of them have to download at least 10 megabytes of text data (both of these numbers are far too high), you are at ... 0.015 "4k blurays per second". Yeah I think MS's datacenters will survive.

A single-page app is not serving "static files". It might serve an initial bundle, but literally everything after that is dynamically generated. There's no way you could serve those responses via a CDN.