Why is Office 365 still so slow?

I have been using Office web apps since 2013. The speed has improved in recent years. But it is still much slower than its rivals.
Even the desktop Office apps are not as fast Google Suite when opening a document from OneDrive. It typically takes over 5 seconds to properly load a document which is not available in the local drive. OneNote sometimes needs ridiculously long time to synchronize. Even for modern apps like Teams, there are occasional lagging problems (e.g. updating the newest chat messages). Being the world's 2nd leader in cloud computing, Microsoft has already built huge infrastructure all over the world. So the problem should be on the software side instead of the hardware side.