How are they able to serve so many people?
Well this is fairly a basic question
Hm, I hate to say it, but it is not a too SMART question.
this is like asking "ok, I have a car, but when I want to transport many many more people it is too small, how to large companies do that" - by NOT USING A CAR.
Similar, web hoster DO NOT USE A SLOW HOME CONNECTION.
Is that not OBVIOUS?
They have data centers and connectivity there is not handled in "I have a DSL connection" but "I Have backhaul connections that may be many many 10gigabit connection". Simple like that.
They use more bandwidth.
In the data center my servers currently are they have more than 110 gigabit link capacity.
Funny you have to ask- you don't ask about te3chnology, but ask about how they do it when a normal home connection is too slow.