Good questions. For a full and thorough description of what is going on here - I will point you to Ilya Grigorik's book "High Performance Browser Networking" https://hpbn.co
Check out chapter 1 and chapter 10 (in fact figure 10-5 may help a lot here.)
When data is coming to your computer, let's describe the connection as a pipe. Bandwidth is "how big" the pipe is. Latency is "how long" the pipe is, and describes how much time the data spends in the pipe before it gets to you.
There are a lot of reasons that developers distribute their content to data centers around the world, but reducing latency is a big reason. If I am in Seattle - and the file I want is in London - it takes longer to travel the pipe than if it were in San Francisco.
Now - every time you open a connection to a new server - there are 3-5 round-trips of packets between your computer and the server before any data is sent. Let's assume each round trip is 25ms... say 100ms per connection to a server.
If you are watching a video - you "pay" the connection startup of 100ms once - and then your video can stream at 50 MBPS. If you are opening a webpage - with >100 requests (but from 20 different servers) - you have to pay this connection setup cost 20 times. Let's say the webpage is 2 MB - which gives us averages of 20 KB per request/100KB per connection.
So if you have 100 KB at 50 MBPS - 50/8 = 6 Megabytes per second - it takes around 16 ms for the files to download (per connection). But you also have this 100ms "connection time" - which dwarfs the file download time. Even if all 2Mb are on 1 server - you have 100ms to set up the connection, and 320ms to download (~25% due to latency). And that is what is making websites slow.
This chart from Ilya's book also will help:
Your last question on research - yes everyone here is looking into how to make webpages faster. However, everything described above is much more complicated, and the way a webpage is built will also have an effect on how long the page loads. Finally - even if a website loads fast for people on 1GBPS internet - it also has to load fast for their customers on cruddy hotel Wi-Fi or on a 2012 Samsung S3.