That's what happens when you employ over-enthusiastic developers obsessed with their Javascript-framework-legacy. Things worked fast when HTML was the UI, and the logic was in the server.
I worked on a server rendered project in the 00s. There was a screen that took 7 minutes to render for about 100 list items.
You can make anything slow if you really try.
Correction: you can many anything slow if you don't try.
Facebook also makes heavy use of frontend frameworks but all their stuff is fast because they are competent at it.
I just measured an uncached page load of facebook.com and it takes 3.5s which isn't stellar.
It doesn't really matter how fast an uncached page load is for Facebook. Why would they optimize it? A user will only see that a few times a decade when they get a new computer. It would be like trying to shave seconds off of a native app install time.
Slow servers are a thing too you know.
At least if the server is slow it's likely to be slow for everyone
I find it's easier to collect metrics from my gear - than from the web-client - so, I can diagnose.
For Google, it's better when it's my CPU doing the work, than theirs.