Why does it take certain websites so long to load?
The issue might be with the servers for those websites. If that is the case, the source of the slowdown most likely is:
The host server:
That is the computing device from which that website is sending you data. It might not be powered well enough or configured properly for the number of people using it or for high-usage periods.
The host server's internet connection:
The data transmission lines that the website's server uses might be jammed by a lot of users at particular times of day, or the user might need additional transmission lines for all the data it has to deliver.
Routers on the internet:
Typically, information passes through several routers to deliver information from a website to you. If one of them is having trouble pointing the information from one place to another, it can slow the delivery of the information you are trying to access.
These issues must be resolved by those responsible for the website:
They are likely aware of the problem, but if you cannot access the site you might want to try another communication channel.