[Fabricio20]

It seems that, at least in reddit's case, the issue is preloading a lot of stuff that on the old website wasn't preloaded. Like videos.

Ben Awad[0] made a quick technical comparison between the two websites and this was his conclusion.

[0]: https://www.youtube.com/watch?v=4jkSiIBDDZ8

[pantalaimon]

That's also what makes it pretty much unusable when you are on a slow mobile connection